The owner of a Hong Kong bulk carrier that is spilling oil in the Solomon Islands has issued an apology over the environmental disaster amid reports the cleanup bill could total $5m.

Seventy five tonnes of oil has leaked so far on the doorstep of a world heritage site on Rennell Island. There’s 600 tonnes still on board the vessel.

The MV Solomon Trader had been loading bauxite from a mine on the island in the days before Cyclone Oma pushed it aground on a coral reef, in the early hours of 5 February.

“The insurer and owner of the grounded MV Solomon Trader have offered a sincere apology to the people of the Solomon Islands following the bauxite carrier’s grounding on a sensitive reef near Rennell Island,” insurer Korea Protection and Indemnity Club and Hong Kong owner King Trader Ltd said in a statement.

The companies said that although matters of liability are yet to be determined, they “expressed deep remorse” and characterised the situation as “totally unacceptable”.

The Solomon Islands Maritime Safety administration says it is investigating a possible breach of the international safety management code because of a “lack of a crew posted on lookout/watch during that night”.

A shipping expert has warned there could be huge insurance ramifications for a code breach including insurers walking away from a claim. This could create headaches over who gets stuck with the cleanup bill.

Reports of the Solomon Trader “crew being absent from the vessel or intoxicated at the time of the grounding are false”, the statement said.

Two maritime investigators will travel to the island next week to conduct interviews with witnesses.

King Trader defended the speed of the salvage process, saying it had secured a local tug to try to remove the vessel in a timely manner. “However, the situation worsened with the arrival of Cyclone Oma, which pushed the stricken vessel harder into the reef resulting in hull and engine room damage,” the statement said.

“The remote and hazardous location has made it difficult to secure local resources and it’s been time-consuming bringing in resources from other locations,” the statement said.

“Inclement weather has made it difficult and at times impossible to access the vessel, and conditions have been too dangerous for external underwater inspections.”

Salvage divers are on standby to inspect the hull and plug holes.

“These activities can only be done when deemed safe, as per weather and tidal conditions and in accordance with international maritime health and safety protocols,” the statement said.

The companies said the ransacking of the vessel had been another setback because special equipment had been removed that would have assisted with the early response.

There was a restoration of some onboard power Tuesday which enabled a deck crane to lift key salvage equipment on board.

The remaining fuel oil onboard is being transferred to higher tanks. There are hopes to pump it to a barge which is due to arrive shortly from Vanuatu.