The ill-fated MV Rena has split in two, but the ship could still be joined together under the surface, the New Zealand Herald reported.

Rena struck and got wedged in on Astrolabe Reef in Bay of Plenty off Tauranga in New Zealand on October 5 last year. Its collision resulted in an oil spill which NZ maritime authorities have managed since then.

Maritime New Zealand on Monday told the Herald the gaping crack in Rena's hull had widened due to bad weather that caused swells of up to 5m on Saturday.

Two cargo containers are confirmed to have fallen overboard on Saturday while a further nine have been "misplaced,'' reports the maritime sources.

While wildlife authorities have managed to rescue animals affected by the oil spill at its peak, there are still a few that needs attention due to the damages added by the ill weather.

Four oiled blue penguins were collected in the past two days, which would be sent to the wildlife recovery centre later this week, while one oiled blue penguin was found dead. One dotterel, two grey faced petrels and 17 penguins are in care at the Massey facility in Palmerston North, the Herald reports.

Environment Minister Nick Smith had said Rena is New Zealand's worst maritime environmental disaster, with oil expected to wash-up on shores for months since October.

Winds of between 10 and 20 knots and swells of 1-2m hit the Bay of Plenty Monday morning, and thunderstorms were reported possible in a forecast until midnight.

Episodes of bad weather since October have hampered container removal operations.