A methane gas leak aboard a cruise ship killed three crew members and injured 10 others as passengers got off the ship after their return from Mexico, authorities said.

No passengers were harmed in the accident Friday at Port of Los Angeles.

The injured crew members from the Monarch of the Seas (search) were taken to hospitals for treatment of minor injuries, fire spokesman Lou Roupoli told reporters.

A statement from the Royal Caribbean (search) cruise line said that five crew members were taken to hospitals and all were in good condition.

The discrepancy was not immediately explained.

The accident occurred after the ship returned from a cruise with about 2,500 passengers and 850 crew members aboard, Roupoli said. The ship makes regular trips down Mexico's Pacific coast.

Royal Caribbean said crew members were replacing a section of pipe connected to the ship's sewage system. The broken line spilled about five gallons of raw sewage and an unknown amount of methane gas in a propeller shaft tunnel, Roupoli said.

Royal Caribbean said the Coast Guard and local authorities were immediately notified and that the cruise line will fully assist in the investigation.

Passenger Yvonne Powers of Sacramento said she was about to disembark with her daughter when she saw men in hazardous-materials protective gear going downstairs.

"Nobody said anything to us," Powers said.

Later, after they had left the ship, there was a public address announcement that there had been a mishap and that "we've got it under control," she said.

The Monarch of the Seas was scheduled to depart later Friday on a cruise to the Mexican port of Ensenada.

The 14-year-old Monarch is based in Los Angeles harbor. Registered in the Bahamas, it and can carry up to 2,744 passengers and 856 crew, according to the company's Web site.