He said the public were being ordered to stay away from the area as the water was "highly toxic" and a danger to their health.
Teams were now arriving at the beach to assess how to carry out a clean up, he said.
"There are teams that are responding as these reports are coming in and being confirmed. They are just asking us to please keep the public out of the way."
Mr Henderson said Mt Maunganui Beach was the only confirmed oil spill site so far.
A Bay of Plenty Times photographer described the oil at the Mount Main Beach as "thick in consistency'' and in clumps.
Many people were out on the beach looking at the oil, he said.
Newstalk ZB reporter James Williams said there were also globules scattered along the sand above the water line near Tay street.
He said there were little patches of oil 3-4cm in width.
Bad weather halts efforts
Earlier bad weather halted efforts to pump 1700 tonnes of oil from the stricken container ship.
Crews aboard the barge 'Awanui' had pumped 10 tonnes of oil from the Rena since 8:30pm last night.
They were called off this morning due to safety concerns amid "changing weather conditions" at the reef.
Maritime New Zealand (MNZ) said the urgent salvage operation had to be stopped if there were any fears for the safety of the 25-strong salvage team on board Rena.
It said the salvage operation at the Rena was urgent and said the crews were looking to resume pumping soon.
"This is an incredibly quick response for a salvage operation.
"The safety of the salvage team and crew remains paramount. If conditions worsen we will temporarily stop the operation until it's safe to resume. Until then they will continue to pump fuel off the vessel for as long as it's safe to work."
The salvage operation would likely begin again later today - and would carry on "around the clock", Maritime New Zealand said.
Urgent action needed
Oil needed to be transferred from the ship urgently because forecasts were for more bad weather in the coming days, it said.
"The weather is expected to deteriorate in the coming days, so we are working around the clock to remove the oil. The weather will impact on both the salvage and oil recovery effort."
MetService has issued a severe weather watch for the Bay of Plenty, with strong northeasterly gusts and heavy rains possible in the region today.
Forecasts issued to MNZ predicted increasing north-easterly winds impacting its salvage
operations in the coming days.
Oil removal likely to take significant time
Transport Minister Steven Joyce said the effort to remove oil from the MV Rena before it causes an ecological catastrophe is likely to take a long time.
"Assuming we're able to get the oil off in a certain time, I've heard weeks and even months in terms of the salvage of the containers and the ship - it's going to be a fair bit of work over a long period of time," he told the Herald.
Prime Minister John Key said his advice was that oil would start arriving on Bay of Plenty's Papamoa beach on Wednesday.
People were being advised not to collect seafood.
PM, authorities seek answers
He has joined Mr Joyce and a growing chorus of others demanding to know how the Rena struck the wildlife-rich Astrolabe Reef early last Wednesday morning.
"I think the first thing you'd have to say is this is a very large ship that, in calm waters, has hit a well-documented reef," Mr Key said.
"So some serious questions need to be asked about why that happened and who is responsible, and there are two inquiries under way to get those answers.
"Obviously the Government is very keen to understand how such a catastrophe could take place."
The three crew members on duty at the time were being spoken to.
There was less oil visible on the water than seen previously, although the situation was likely to worsen with winds picking up over coming days.
Boats were using a large skimmer to scoop up the oil last night.
Maritime New Zealand's national on scene commander, Rob Service, could not say how long it could take to clean oil from the shoreline.
Penguins suffering as slick worsens
An oil-coated little blue penguin yesterday became the ninth seabird to be recovered and processed at the oiled wildlife response centre - a base of tents, tanks and makeshift laboratories set up at Mt Maunganui capable of taking up to 500 birds.
The little bird appeared back to its lively self after it was dropped in a pool and began happily swimming around, delighting Conservation Minister Kate Wilkinson and photographers.
Co-ordinator Kerri Morgan expected to see many more cases of affected wildlife. Two hundred volunteers were standing by to help.
Brett Gartrell, Massey University's Wildlife Facility Director, told Newstalk ZB there is no way to tell how many more birds could be affected, but they have experts on standby to deal with up to a thousand.
He said 10,000 Grey Faced Petrels are in one area near the Rena, and thousands of Diving Petrels in another. There are also between 200 and 300 Little Blue Penguins around the area.
Mr Gartrell said they are able to get a projection of where the oil is headed, so they all scare the birds away from those areas.
"One is to just be having lots of boats and people and activity there but we also use things like air horns and whistling tape that we put up that moves in the wind and gives off a high pitch whistling noise."
He said as for marine mammals like dolphins, they can put sonic devices in the water to make noises to get them away.
Huge team working to stem spill
The team dealing with the salvage, led by Dutch specialists Svitzer, had 250 workers.
Two more barges to recover heavy fuel oil in the water were on their way.
The New Zealand Defence Force has provided specialist staff, two shore patrol vessels, Seasprite and Iroquois helicopters, a C-130 Hercules sent to pick up equipment from Australia, a dozen specialist staff and the HMNZS Endeavour, which arrived at Tauranga last night for use as a potential command centre.
A further 300 army staff were on stand-by.
Mr Key rejected criticism over response efforts by environmental groups, the Green Party and Labour, who are calling on the Government to take over.
"We've had a plan, it has been activated and mobilised, and all I can say is that I asked international experts whether we were acting quickly enough and if there was anything else we could do - and the assurance I've been given is it's relative to other accidents around the world and we've been acting very quickly."
FOUR OPTIONS
1. Dispersant:
The chemical Corexit 9500, used to tackle BP's disastrous spill in the Gulf of Mexico last year, is being sprayed to break up the black oil. But it is not clear whether it is working, and international experts are measuring the results.
2. On-Water Recovery:
Scooping up oil from the water, also being tried, is a weather dependent and largely ineffective approach. In most instances, less than 10 per cent of the oil is recovered.
3. Protection Booms:
Many are asking why booms aren't being used to ring-fence the leaked oil. But conditions such as strong currents, deep water and wave action have made it impossible to use them.
4. Shoreline Clean-Up:
The least preferred - but ultimately inevitable - option, with oil due at Papamoa Beach on Thursday. Removing oil from sandy beaches was considered far easier than from areas such as rocky foreshores
By Newstalk ZB, APNZ and NZ Herald staff
