New Zealand says an oil spill from a grounded cargo ship off its northern coast is now the worst environmental maritime disaster it its history.

The Liberian-flagged Rena has been leaking fuel oil since striking a reef on Wednesday in the Bay of Plenty. Maritime New Zealand says between 130 and 350 tons of oil gushed from the container vessel's ruptured hull over the last 24 hours as the ship was tossed by high waves and strong winds.

New Zealand Environment Minister Nick Smith described it as the most serious incident of its kind that the country has faced.

A salvage crew was on board the Rena working to transfer the 1,700 tons of fuel oil from the ship's tanks to another vessel. But the crew had to be evacuated Tuesday because of the bad weather, and the on-scene commander, Nick Quinn, said that has set back the clean-up effort.

Health officials have ordered residents to stay off the beaches and out of the sea, and not to touch anything with oil on it.