The MV Solomon Trader got stuck on a reef on Rennell Island in early February, and began leaking oil

The Maritime Executive reported that salvors had removed 230 tonnes of bunkers out of an estimated 600 tonnes on board.

However, the existing spill is worse than it previously estimated, according to shipowner King Trader and its insurer Korea P&I.

In a statement the companies said the amount leaked is more than that of initial estimates of some 70 tonnes of oil

They said that will be clarified as the response progresses.

At least five kilometres of reefs and coastline have been soiled with fuel oil, and estimates of the cost of cleanup range as high as $US50 million.

The ship's charterer, bauxite mine operator Bintan Mining, claims that it bears no responsibility for the casualty, and its operations continue.

The Solomon Islands' acting prime minister, Rick Hou, has threatened to "blacklist" the companies involved if they "do not take on their responsibilities."

Salvors including specialists from the US and Australia are in the country helping with the salvage operation.