Authorities say six people have been sickened by carbon monoxide aboard a cruise ship docked in Baltimore.

Baltimore fire department spokesman Chief Kevin Cartwright says crews are on the scene to treat the victims. A hazmat team is trying to determine where the leak is coming from.

Cartwright didn't know how ill the victims are or whether they were crew members or passengers. It's also unclear how many people were on the ship.

The incident occurred aboard the Celebrity Mercury cruise ship.