HOUSTON (Reuters) - Nearly a fifth of crude oil production and 28% of natural gas output in U.S. Gulf of Mexico federal waters remained offline in the aftermath of Hurricane Francine, the U.S. offshore energy regulator said on Sunday.

Francine tore through prime offshore oil and natural gas producing areas and slammed into Louisiana as a Category 2 hurricane on Wednesday. The storm toppled trees, flooded coastal areas and cut power in four southern states.

Energy producers had shut-in 338,690 barrels per day of oil production and nearly 515 million cubic feet of natural gas from Gulf waters, the Bureau of Safety and Environmental Enforcement estimated from producer reports.

(Reporting by Gary McWilliams)