The United Nations on Tuesday began siphoning one million barrels of oil from a decaying supertanker off the coast of war-torn Yemen, a crucial step in the race against time to prevent a potential environmental disaster.

The supertanker, the FSO Safer, became a symbol – thanks largely to UN efforts – of the need for urgent action to avoid massive damage to the marine ecosystem in an area that is home to key global shipping lanes.

The stranded rusting vessel holds four times the amount of oil spilled by the Exxon Valdez – enough to make it the fifth largest oil spill from a tanker in history.

“The United Nations has begun an operation to defuse what might be the world’s largest ticking time bomb. This is an all-hands-on-deck mission and the culmination of nearly two years of political groundwork, fundraising and project development” said UN Secretary-General António Guterres.

Lying north of the Yemeni port Hudaydah, UN officials have warned for years about the possibility that the 47-year-old tanker could crack and explode.

The UN Development Programme (UNDP) warned that a massive spill from the Safer would destroy swathes of marine life in the Red Sea.

Speaking to reporters in Geneva, spokesperson Sarah Bel expressed concern for the fishing communities on Yemen’s Red Coast, already living in a crisis-wracked situation, as a spill would like ‘wipe out 200,000 livelihoods instantly” and “fish stock would take twenty five years to recover.”