The captain and navigation officer of a ship that caused one of New Zealand's biggest sea pollution disaster when it ploughed into an offshore reef have been sentenced to seven months in prison.

Prosecutors told the Tauranga District Court on Friday that the pair ignored basic navigational practices when they attempted to take a short cut to reach port on October 5 last year.

The Filipino officers were in charge of the Liberian-flagged Rena when it hit the reef last year, releasing an oil slick that killed thousands of sea birds and fouled beaches in the North Island's pristine Bay of Plenty.

Captain Mauro Balomaga and navigation officer Leonil Relon had pleaded guilty in February to a range of charges, including attempting to pervert the course of justice by altering navigation records after the accident.

They also admitted operating a ship in a dangerous manner and discharging harmful substances from the cargo vessel.

Keith Manch, the maritime New Zealand director, welcomed the sentences, saying the ship's officers had to be held accountable for their actions.

"This grounding has had significant consequences for the Bay of Plenty community and the country as a whole," he said.

"Today marks a milestone in the response, which is still under way."

The Rena hit the Astrolabe Reef 22km offshore in clear conditions as it steamed at full speed towards Tauranga, New Zealand's largest container port, becoming stuck on the submerged rocks.

Toxic fuel

More than 300 tonnes of toxic fuel oil spewed from the vessel, creating an oil slick kilometres long, which washed onto beaches at the popular tourist spot, coating birds in thick black sludge.

Nick Smith, the environment minister, described it as New Zealand's worst maritime pollution disaster.

The accident triggered a dangerous salvage operation which involved crews scrambling to pump the remaining oil from the Rena's fuel tanks as heavy seas pounded the stricken vessel and opened up deep cracks in its hull.

An army of 5,000 volunteers was mobilised to clean up the shoreline of the bay, which contains marine reserves and teems with wildlife including whales, dolphins, penguins, seals and rare sea birds.

The vessel eventually broke up on the reef in January and the stern sank, further complicating a salvage operation which is still continuing after eight months, as crews remove shipping containers from the bow.

Manch said Balomaga and Relon had altered the Rena's course without plotting what lay ahead and failed to recognise how hazardous the reef was when it showed up on the ship's radar, dismissing it as a false echo or small vessel.

The government has estimated the disaster clean-up will cost $98m (NZ$130m), most of which will be covered by the Rena's owner, the Greece-based Costamare Shipping Company, and its insurers.

Source: Agencies