Four people were in critical condition after a fire hit a giant Exxon Mobil refinery in Baton Rouge, Louisiana, on Tuesday, a local hospital said.

The incident was the fourth in two days to hit Gulf refineries, cutting fuel production in the region at plants with combined capacity of over 1 million barrels per day.

Exxon said the fire was extinguished around 4 p.m. local time and the company had accounted for all staff at the refinery.

Baton Rouge General Hospital said four people in critical condition were admitted to the regional burn unit, a hospital spokeswoman said.

The fire broke out at an 18,750-barrel-per-day alyklation unit, which produces high-octane gasoline components, as five people prepared to restart it following repair work, sources familiar with the plant's operations said.

A compressor blew out during the restart attempt, the sources said, setting off the blaze.

Two operators and two contractors were injured, the sources said. The two operators are women.

An Exxon spokesman said details of the fire were under investigation. The refinery is the fourth-largest in the United States, with capacity to refine 502,500 barrels per day in crude oil.