The United Nations said on Tuesday it had started the removal of more than 1 million barrels of oil from a decaying supertanker off Yemen’s Red Sea coast.

UN officials have been warning for years that the Red Sea and Yemen’s coastline was at risk as the Safer tanker could spill four times as much oil as the 1989 Exxon Valdez disaster off Alaska.

The war in Yemen caused the suspension in 2015 of maintenance operations on the Safer, which is used for storage and has been moored off Yemen for more than 30 years.

The UN has warned its structural integrity has significantly deteriorated and it is at risk of exploding.

“In the absence of anyone else willing or able to perform this task, the United Nations stepped up and assumed the risk to conduct this very delicate operation,” UN Secretary-General Antonio Guterres said.

“The ship-to-ship transfer of oil which has started today is the critical next step in avoiding an environmental and humanitarian catastrophe on a colossal scale.”

The oil transfer is expected to take 19 days to complete, the UNDP said in a statement.