The skipper of container ship Rena, which ran aground off Tauranga in New Zealand's worst maritime environmental disaster, is due to be sentenced in Tauranga District Court on Friday.

The 44-year-old Filipino man, who has name suppression, pleaded guilty to wilfully attempting to pervert the course of justice by altering the ship's documents after it grounded in October last year. The charge was laid under the Crimes Act and carries a maximum penalty of seven years in prison.

He has also pleaded guilty to other charges. Under the Maritime Transport Act he was charged with operating a vessel in a manner causing unnecessary danger or risk and under the Resource Management Act - where the heaviest penalty is two years in prison and a $300,000 fine - he was charged in relation to discharging harmful substances from a ship.

In New Zealand's worst maritime environmental disaster, the cargo ship Rena grounded on Astrolabe Reef, Tauranga, spilling containers and about 360 tonnes of oil, which washed up on local beaches and killed wildlife.

The clean-up operation is still being carried out and the ship, still stranded on the reef, has split in two and the stern section has sunk.