Emergency services attend an incident at Parson Green underground station. Photo / AP
KEY POINTS:
An explosion on a packed train in Parsons Green, southwest London has left several passengers with facial burns
London's Met Police says the explosion has been declared a "terrorist incident"
Witnesses describe "madness", a "wall of flame" and "a really hot intense fireball"
Incident happened during morning rush hour
No arrests made yet
22 people taken to hospital
A Kiwi has described how panicked passengers ran from the Tube train in South London after an explosion left several people injured.
People fled in panic after a "fireball" reportedly left several passengers with facial burns on the packed train in Parsons Green, west London.
Scotland Yard say it was a terror attack but could not confirm claims there is another device and the suspect is on the run - but an officer at the scene told MailOnline: "We believe there is a second bomb - there is a man with knives on the loose."
The Met’s Counter Terrorism Command are investigating after the incident at #ParsonsGreen tube station is declared a terrorist incident
The 32-year-old from Napier, who lives in Putney, didn't hear anything because he had been wearing his headphones.
He had to exit the station with the other passengers, and saw all the emergency services.
"It was madness."
The Ministry of Foreign Affairs and Trade said there was no indication at this stage of any New Zealanders being injured and the NZ High Commission in London hasn't received any requests for consular assistance.
Prime Minister Theresa May has described the attack as "cowardly" and said her thoughts are with those who have been injured.
"Clearly this was a device that was intended to cause significant harm," she said.
British Foreign Secretary Boris Johnson says people should "keep calm and go about their normal lives" as emergency services respond to an incident at a London subway station.
Johnson says it would be "wrong to speculate," and that police and transit authorities "are on it".
The mayor of London says the city "will never be intimidated or defeated by terrorism".
Sadiq Khan says the city "utterly condemns the hideous individuals who attempt to use terror to harm us and destroy our way of life".
He says Londoners should remain "calm and vigilant" after a fire on a subway train that police are calling a terrorism incident.
Khan says he will be attending a meeting of the government's COBRA emergency committee with Prime Minister Theresa May later.
United States President Donald Trump has shared his thoughts on Twitter saying Scotland Yard need to be more proactive and that these "loser terrrorists need to be dealt with in a tougher manner".
Another attack in London by a loser terrorist.These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!
London has been targeted by attackers several times this year, with vehicle attacks near Parliament, on London Bridge and near a mosque in Finsbury Park in north London.
Police are hunting for the "bucket bomber" who tried blow up a rush hour Tube train amid claims the terror suspect is armed with knives and may have left other devices.
The crude device could have killed dozens but failed to properly detonate and sent a "wall of fire" through the carriage injuring at least 18 people including a ten-year-old boy.
One witness told the BBC there was a "bang" and then a "wall of flames", which spread through the packed carriage.
The doors opened at Parsons Green and the commuters, many of them with scorched faces and hair, ran off screaming.
Pictures from the District Line train appear to show a burning plastic bucket stashed in a Lidl carrier bag.
Photographs show what experts believe is a "pretty unsophisticated" bomb in a flaming white bucket inside a Lidl freezer bag with Christmas lights connected to a battery protruding out of the top.
The BBC said that it had a timer, suggesting the bucket bomber left in on the train and fled before it exploded.
There were reports of a man at the station with a knife in the aftermath of the explosion. Scotland Yard said they believe this is unrelated to the Tube incident but are investigating and urging people to avoid the area.
Sophie Raworth, the BBC News presenter who was at the scene, said she saw a woman on a stretcher with burns to her face and legs.
"I spoke to a woman, Laura Bishop, who said she was standing there and all of a sudden heard a bang - and saw a wall of flames, flames in the carriage," she said.
"She saw people who had burns on their hair, burns on their head and the doors opened immediately."
Ms Raworth added: "I have just seen a woman who was just stretchered off here and clearly her legs are wrapped up and she has burns.
"She had burns to her face - she's conscious, she was taking oxygen and pain relief as well.
"She seemed to have burns all over her body from top to toe."
Speaking on the Victoria Derbyshire show, she told how a witness told her there was a stampede and then "panic, just complete panic".
She added: "There are a lot of people here at Parsons Green looking very anxious and worried, trying to work out what has happened. Clearly just trying to get out of the station itself was pandemonium."
Media technology consultant Richard Aylmer-Hall, 53, was sitting on the District Line train bound for central London when panic unfolded at around 8.20am.
He said he saw several people injured, having apparently been trampled as they tried to escape. He told Telegraph UK:
"I was blissfully reading my paper and listening to a podcast and suddenly the whole world charged past me down the platform, down the Tube.
"I was on the Tube, we had just stopped at Parsons Green, I was on my way up from Wimbledon towards Paddington and suddenly there was panic, lots of people shouting, screaming, lots of screaming.
"There was a woman on the platform who said she had seen a bag, a flash and a bang, so obviously something had gone off.
"It was an absolutely packed, rush-hour District Line train from Wimbledon to Edgware Road.
"I saw crying women, there was lots of shouting and screaming, there was a bit of a crush on the stairs going down to the streets.
"Some people got pushed over and trampled on, I saw two women being treated by ambulance crews.
Horrified witnesses on social media claim people are "screaming and running off trains".
A witness on Twitter said there were explosions in Parsons Green district line train.
"Fireball flew down carriage and we just jumped out open door."
Emma Stevie tweeted: "I'm safe - just had to run for my life at #ParsonsGreen station - huge stamped, lots injured. Not sure why - fire/explosion mentioned."
Ben Lee wrote: "Just been evacuated at #parsonsgreen - panic from rearmost carriage - pax saw smoke but NO injuries"
Another social media user said: "What's happening at Parsons Green, panic on the platform reports of fire or explosion in a bag. No announcements."
A London Fire Brigade spokeswoman said: "We were called at 8.21am (local time) and we have information there was a fire on a train eastbound at the platform at Parsons Green.
"We have got two fire engines there."
The Met Police tweeted: "We are aware of an incident at Parsons Green station. Officers are in attendance. More info ASAP."
We are aware of an incident at #ParsonsGreen tube station. Officers are in attendance. More info ASAP
The London Ambulance Service also says it is on the scene, tweeting: "We are on scene alongside the Met Police at Parsons Green. More information to follow."
"We have sent multiple resources to the scene including single responders in cars, ambulance crews, incident response officers and our hazardous area response team, with the first of our medics arriving in under five minutes.
"Our initial priority is to assess the level and nature of injuries. More information will follow when we have it."
The incident is being investigated by counterterrorism authorities and is the latest attack in Europe in recent years. Here are some of the other major ones:
•Aug. 17, 2017: A van attack kills 14 people in Barcelona, while another person was stabbed to death by the attacker as he fled. Another attack in nearby Cambrils a day later leaves one dead. The attacks were claimed by the Islamic State group. •June 19, 2017: A British man who had reportedly made anti-immigrant and anti-Muslim remarks drives into a crowd of worshippers outside a London mosque. One person dies and nine others are wounded. •June 3, 2017: Three Islamic extremists drive into a crowd of pedestrians on London Bridge and then go on a knife rampage in nearby Borough Market, killing eight people and wounding dozens of others. •May 22, 2017: A suicide bomber kills 22 people and injures dozens during an Ariana Grande concert at Manchester Arena in northern England. •April 7, 2017: A man driving a hijacked beer truck hits pedestrians at a Stockholm department store, killing four. •March 22, 2017: A man drives his rented SUV into pedestrians at London's Westminster Bridge, killing four, before stabbing a police officer to death. •Dec. 19, 2016: A hijacked truck plows through a Christmas market in Berlin, killing 12. •July 14, 2016: A truck driver targets Bastille Day revelers in Nice, killing 86. •March 22, 2016: Suicide attacks on the Brussels airport and subway kill 32 and injure hundreds. The perpetrators have been closely linked to the group that carried out earlier attacks in Paris. •Nov. 13, 2015: Islamic State-linked extremists attack the Bataclan concert hall and other sites across Paris, killing 130 people. •Feb. 14, 2015: A gunman kills Danish filmmaker Finn Noergaard and wounds three police officers in Copenhagen. A day later the gunman, Omar El-Hussein, attacks a synagogue, killing a Jewish guard and wounding two police officers before being shot dead. •Jan. 7-9, 2015: A gun assault on the Paris offices of the satirical magazine Charlie Hebdo and an attack on a kosher grocery store kill 17 people. Al-Qaida in the Arabian Peninsula claims responsibility for the attack, saying it was in revenge for Charlie Hebdo's depictions of the Prophet Muhammad.- •May 24, 2014: Four people are killed at the Jewish Museum in Brussels by an intruder with a Kalashnikov. The accused is a former French fighter linked to the Islamic State group in Syria. •May 22, 2013: Two al-Qaida-inspired extremists run down British soldier Lee Rigby in a London street, then stab and hack him to death. •March 2012: A gunman claiming links to al-Qaida kills three Jewish schoolchildren, a rabbi and three paratroopers in Toulouse, southern France. •July 22, 2011: Anti-Muslim extremist Anders Behring Breivik plants a bomb in Oslo then launches a shooting massacre on a youth camp on Norway's Utoya island, killing 77 people, many of them teenagers. •Nov. 2, 2011: The offices of Charlie Hebdo in Paris are firebombed after the satirical magazine runs a cover featuring a caricature of the Prophet Muhammad. No one is injured. •March 2, 2011: Islamic extremist Arid Uka shoots dead two U.S. airmen and injures two others at Frankfurt airport after apparently being inspired by a fake internet video purporting to show American atrocities in Afghanistan. •July 7, 2005: Fifty-two commuters are killed in London when four al Qaida-inspired suicide bombers blow themselves up on three subway trains and a bus. •March 11, 2004: Bombs on four Madrid commuter trains in the morning rush hour kill 191 people.
- additional reporting NZ Herald, Telegraph UK, AP