By the CNN Wire Staff

January 8, 2012

In this handout provided by Maritime New Zealand, MV Rena is seen in two pieces after overnight bad weather pounded the vessel, on January 8, 2012 in Tauranga, New Zealand.

(CNN) -- A cargo ship that ran aground on a reef off the coast of New Zealand last year has split in two, spewing debris and triggering the possibility of a new oil spill, officials said Sunday.

Hundreds of tonnes of oil have already leaked from the ship, leading New Zealand's environment minister, Nick Smith, to call the spill the country's most significant maritime environmental disaster.

The sections of the ship, which are about 20 to 30 meters (65 to 98 feet) apart now, remain on the Astrolabe Reef.

The Rena, a Liberian-flagged vessel, struck the Astrolabe Reef, about 12 nautical miles off the city of Tauranga, on the North Island, in October.

"While reports at this stage indicate there has not been a significant release of oil, with the Rena in its current fragile state, a further release is likely. While it is unknown at this stage exactly how much oil may be released, teams have been mobilised and will be ready to respond to anything that may come ashore. The wildlife response had also been increased to help deal with any affected wildlife," Maritime New Zealand officials said in a statement.

Bad weather, which caused the ship to break, is expected to continue for the next three to four days, the agency said.

At least 23 containers from the ship have been confirmed lost as a result of the split, while another seven are thought to be in the water, officials said. Debris surrounds the wreck.