A chlorine leak Monday night at a chemical plant on this city's waterfront injured 12 people and prompted the evacuation of the surrounding industrial area, a fire official said.

Deputy Fire Chief Jolene Davis said a dozen people were transported for medical treatment but she could not offer any information on their condition because of privacy restrictions.

The leak at Pioneer Americas Inc. occurred as workers were filling a 1,000-gallon tank with liquid chlorine shortly before 7 p.m., Davis said.

Firefighters evacuated workers and others from an area roughly bordered by 11th Street, Milwaukee Way, Highway 509 and Port of Tacoma Road, she said.

Emergency crews were monitoring the area late Monday night for the presence of chlorine gas in the air.

Normally a gas, chlorine becomes liquid under pressure. It is toxic and causes respiratory problems if inhaled.