International Maritime Organization secretary general Kitack Lim has called for governments to back a United Nations’ project to lighter oil from a decaying floating storage and offloading (FSO) vessel off Yemen.

The UN has drawn up a plan to transfer oil off the 407,000-dwt FSO Safer (built 1976), which is loaded with 1.14m barrels of light crude, and replace it.

Salvors said the ageing FSO Safer is in danger of starting to leak oil.

Lim described the situation as an “impending environmental disaster.”

“We must do all we can to prevent it. We must act now,” Lim said.

A pledging conference has been arranged by the government of the Netherlands and the UN to raise funds.

“The UN has a coordinated plan to mitigate the risk by transferring the oil to a safe temporary vessel. This needs financial resources,” Lim said.

“The time is now. The risks are high. We must act to avert disaster.”

The FSO is owned by Yemen’s Safer E&P Operation Co but has not been operational since March 2015, when the region fell under the control of the Houthi rebels.

The UN has long wanted to get inspectors on board the unit, which is anchored 4.8 nautical miles (8.8 km) off Ras Isa, but so far the rebel Houthi authorities there have not allowed this.

Experts believe a spill of all the oil on board would be four times worse than the worst yet seen — the Exxon Valdez tanker disaster in Alaska in 1989.