At least 20 children among 226 confirmed dead in Mexico quake

Rescue workers and volunteers search a building that collapsed in today's earthquake. Photo / AP

Kiwis living in Mexico have described stumbling out of their buildings into plumes of dust and ash after a 7.1 magnitude quake hit Mexico City and surrounding states this morning.

At least 226 people have been confirmed dead since the quake hit in the Puebla region, including some 20 children after a school building collapsed on them. Another 30 children and eight adults are still missing at the school in the suburb of Coapa.

Rescuers are desperately hunting through the ruins of 44 buildings that had crumbled in the quake, with many more people still missing.

There have been no reports of Kiwi citizens injured, but the New Zealand embassy in Mexico City is monitoring the situation closely, Minister of Foreign Affairs Gerry Brownlee said.

He sent "sympathy and support" to President Peña Nieto and to the people of Mexico and said New Zealand was ready with aid if required.

"New Zealand understands only too well the devastation that is caused by earthquakes," Brownlee said.

"Our thoughts are with the injured, the loved ones of those affected, and the emergency services staff at the forefront of the response."

It was the second powerful earthquake to strike the region in the past fortnight, after an 8.1 magnitude quake off the coast of Mexico killed 90 people.

Rescuers sift through the rubble of the city hall in Juchitan, Oaxaca state, following the deadly 8.1 magnitude quake that hit the country two weeks ago on September 8.

The Government's Safe Travel website told Kiwis to follow the advice of local authorities and let their families in New Zealand know they were okay. Anyone who needed help should contact the NZ embassy in Mexico City.

Jai Krishnan, who is living in Mexico, saw crowds of terrified people in the streets moments after this morning's quake hit.

Krishnan, from Wellington, told Radio New Zealand he rushed to his daughter's school after the quake struck.

He had been in his second-floor Mexico City apartment when the shaking began.

"I actually ran down to my daughter's school, and I ran through plumes of dust and the smell of ash, and I saw lots and lots of people in the street.

"Parts of buildings have collapsed, about 100m from where I live a building has come down on the corner, it probably was six or seven storeys, and it's down to about two storeys now, it's so saddening to see."

Krishnan told RNZ he has lived in the capital with his partner and daughter for the past year.

He said the latest shake was even more terrifying than the deadly earthquake that struck earlier this month.

"There's sirens and helicopters buzzing around all over the place, I went on to the roof of our building and there's smoke pouring out of other buildings across the city."

Kiwi Simon Pierre, who coaches Mexico's Sevens rugby team, was sitting at his desk at the rugby federation when the whole building started shaking.

He shouted "temblor" - the Spanish word for earthquake - and he and workmates rushed down the two flights of stairs and out to the street.

"Even once we were on the street the ground was still moving and it felt slightly like we were on a boat with a bit of a sea swell," Pierre said.

Pierre is from Macandrew Bay in Dunedin but his wife's family lives in Mexico. All are safe and sound but his wife was struggling to get home from Santa Fe due to gridlocked traffic.

"There are some assholes - sorry for the language but that is what they are - taking advantage of the fact that traffic is not moving and the lack of police officers in the street, as they have been moved to the other areas where they are needed most," Pierre said.

"These groups of buggers are assaulting people in their cars and stealing their personal belongings."

Two earthquakes also jolted New Zealand in quick succession today, but a geologist said they were probably not related to the Mexico quake - or to each other.

An hour after a 5.8 magnitude earthquake struck 585km south-west of Invercargill at 1.43pm, the Cook Strait was rattled by a 5.1 quake that struck 30km north-east of Seddon.

GNS seismologist Dr Anna Kaiser said a big quake changes the stresses in the crust in the area, which could trigger aftershocks nearby.

"But obviously that's not a mechanism that could explain the earthquake in the Cook Strait because it was too far away," she said.

The Cook Strait quake was likely another aftershock of November's Kaikoura quake, she said.

There was also nothing to suggest there was any direct link with the major quake that hit Mexico City.