The United Nations has started a operation to remove 1.1 million barrels of oil from a decaying supertanker moored off Yemen's Red Sea coast.
A salvage vessel with a crew of experts reached the FSO Safer on Tuesday.
They will undertake work to make it secure for oil to be transferred to another tanker, Nautica, which is due to sail from Djibouti next month.
There is an imminent risk that the Safer could explode or break apart, causing an environmental catastrophe.
The UN has so far raised $114m (£92m) to pay for the unprecedented project through donations from dozens of member states, private companies and even the general public through a crowdfunding campaign.
But it says another $29m is urgently required, including to safely moor the Nautica to an anchored loading buoy and tow the Safer to a recycling yard.