The oil spilled from a Liberian- flagged cargo ship stranded on a reef off New Zealand shore has become "worst ever" maritime environmental disaster in the country, a senior official said Tuesday.

An oil slick streams from the Rena, a 47,000 tonne container ship grounded on a reef in New Zealand's Bay of Plenty. [Agencies]?

Oil had been pouring out of 47,000-tonne Rena at "fivefold" the rate it had in the days after the ship grounded on Astrolabe Reef, 12 nautical miles offshore, near the port city of Tauranga on Oct. 5, said Environment Minister Nick Smith.

According to Maritime New Zealand, about 130 and 350 tonnes of oil leaked out of the Rena Tuesday morning when the vessel moved and ruptured a main fuel tank, allowing oil to pour out.

About midday, the crew -- understood to be mostly Filippinos -- and salvage teams were evacuated as a precaution following a mayday call. One naval crew member suffered a moderate back injury.

Significant amounts of oil would start washing up around the beach resort of Mount Maunganui from Wednesday and into the coming weeks, said Smith.

The government would hold those who were responsible for the grounding to account, promised Smith.

CLEAN-UP COSTS

MNZ director Catherine Taylor told Radio New Zealand Tuesday it was not thought the ship would break up.

The 236-meter Rena -- reportedly carrying milk powder, timber, meat, fish and a small amount of the hazardous material ferrosilicon -- had 1,700 tonnes of fuel oil on board when it ran aground last Wednesday.

Environmental response coordinator Nick Quinn warned the public to prepare for weeks of clean-up work on beaches in the area around Tauranga.

MNZ, the country's shipping authority, also warned people to stay out of the sea and to avoid touching the oil and eating seafood in affected areas along the east coast of the North Island.

Transport Minister Stephen Joyce said the cost of the Rena clean-up had already risen to millions of dollars.

Much of that cost would be borne by the vessel owners under maritime law, but there would be a cost to the New Zealand government, he said.

COMPLEX SITUATION

Prime Minister John Key on Tuesday rejected mounting criticism that the government had reacted too slowly to the emerging catastrophe.

Oil was likely to be on the beaches "for quite some time," he said, adding it was "too early" to talk about compensation.

"I understand (the shipping company) have significant insurance and I am sure Maritime New Zealand, in due course, will have those discussions.

"There are also two investigations under way and we will need to get those investigations reached, which will probably take quite some weeks and then understand how liability should be apportioned but we will do that in due course."

He described the situation as "very, very serious."

"Eventually, someone will have to accept responsibility for what's gone wrong here."

HEALTH WARNINGS

Teams of some of the 500 people trained to skim the oil off the surface of the beach with the minimum impact headed out to Mount Maunganui and Papamoa beaches wearing special protective garments Tuesday.

MNZ reissued a plea to the public not to join the clean-up: " Although it looks bad, the oil in its clumped state is at no risk of going anywhere, and people attempting to remove it without the proper training or equipment risk making the situation worse."

Extra precautions were also being taken at a number of sensitive sites, and a boom had been deployed at the environmentally sensitive Maketu Estuary.

Local media reported hundreds of people had flocked to the beach Monday and children were even playing with the thick globs of oil.

Health officials warned contact with it could cause skin rashes and the fumes could cause nausea.

MNZ national on-scene commander Rob Service warned people to stay away.

"That's kilometers of beach, it's impossible for us to have a policeman on every pathway going to the beach so we again request the public, please stay off the beach and if you have to go there don't touch the oil."

Meanwhile, officials were waiting for a weather window before resuming the operation of pumping the Rena's toxic fuel oil on to the bunker barge Awanuia.

Strong seas have been battering the area around Astrolabe Reef.

MNZ salvage manager Bruce Anderson said forecasts suggested more settled weather over the next few days.