The Filipino captain of the ship that caused New Zealand's worst maritime environmental disaster has issued a public apology for the catastrophe and for trying to cover up his role.

Mauro Balomaga was deported to the Philippines earlier this month after serving half of a seven-month jail term for operating the container ship Rena in a dangerous manner and attempting to falsify navigation records.

Speaking from the Philippines, Balomaga told The New Zealand Herald of the guilt he felt knowing his actions had caused so much devastation.

The Liberian-flagged Rena ploughed into an offshore reef in October last year, spewing more than 300 tonnes of toxic fuel oil that killed thousands of sea birds and fouled beaches in the North Island's pristine Bay of Plenty.

Nick Smith, then environment minister, had described it as New Zealand's worst maritime pollution disaster as the oil slick spread to the shoreline of the bay, which teems with wildlife including whales, dolphins, penguins, seals and rare sea birds.

"We did not think it would come to that point. Of course we felt sorry about it," Balomaga said in his first public statement about the disaster.

"During the course of the interviews and the investigations, we did apologise on the record, but that was for the safe-keeping of the authorities, and not for the public."

Balomaga admitted taking a short-cut on the way to the Port of Tauranga but said he was surprised that the Rena ploughed into the reef -- even though it had showed up on the ship's radar 15 minutes before the grounding.

"It was really unexpected... We thought we may not be able to save it completely, but we could limit the damage and we could save the ship... That was our thinking initially."

The New Zealand government has estimated the on-going disaster clean-up will cost NZ$130 million ($109 million), most of which will be covered by the Rena's owner, the Greece-based Costamare Shipping Company, and its insurers.