Two hundred more locator beacons will be attached to the MV Rena's fragile container load as officials warn of a "strong likelihood" that further oil will leak from the crippled container vessel.

Salvors aboard the Rena have fixed 35 of the underwater transponders, called "pingers", to containers holding dangerous goods and others likely to tumble overboard.

Salvage master Captain Drew Shannon said the extra 200 being flown in from the United States would be inserted only on those containers that could be safely accessed.

"Obviously those containers which are hard to reach will present unacceptable danger ... we'll start with the first 200 and get them on to as many containers as possible."


As the 20 salvors on board the Rena yesterday began clearing air pockets to offload the last 358 tonnes of oil from the submerged starboard number five tank - a job that would take 100 hours of continuous pumping in the right conditions - a 6000-tonne container barge was successfully tested before the next stage of the lengthy salvage operation.

The ST60, chartered from Australia, carries one 280-tonne crane to lift the containers and another smaller crane which will be used to lift salvors on to the containers to release twist locks connecting them to each other.

The vessel, which will not be used until all of the oil is off-loaded, would be held in place with four anchors and four mooring lines connected to the Rena.

Mr Shannon did not rule out the possibility of using shaped explosive charges to dislodge the containers, but said it was more likely salvors would be able to either safely unlock the bindings or cut through them.

"There have been other container ships placed in similar situations and we are drawing on industry to assist with the method and means of actually removing the containers.

"But every ship is different and with this ship we'll take it as it comes."

About 22,300 litres of oil had meanwhile been pumped into the tug Go Canopus.

"There is still a strong likelihood further oil will be released - but the more oil removed from the ship, the lower the risk," Maritime New Zealand national on-scene commander Rob Service said.

Oil was continuing to resurface in some areas yesterday, and a clean-up force of 70 volunteers and 60 contractors was out on beaches.

Oil reported at Waihi Beach, 60km north of Mt Maunganui, was yesterday found to be algal bloom.

A 50-strong team of wildlife experts remained at the oiled wildlife response centre in Mt Maunganui, where three little blue penguins found on Monday have joined more than 400 birds being held in captivity.