Washington's city police force began putting body cameras to the test Wednesday, making the US capital the latest to use video technology as a routine part of law enforcement.

Under a $1 million program, volunteers within the Metropolitan Police Department will try out five different kinds of body cameras, before the city decides which ones work best.

Plans call for the District of Columbia to acquire 250 cameras, which officers would activate every time they respond to a call or make a traffic stop, police chief Cathy Lanier said.

"It's very rare that we're not being videotaped somewhere by somebody anyway," she told a city hall press conference. "We're the last people to get cameras, right?"

More and more US cities are adopting body cameras, with interest surging after the fatal shooting in August of an unarmed black teenager in a Missouri town that didn't use the devices.

Mayor Vincent Gray said Washington initiated its program about 18 months ago, well before the August 9 killing of 18-year-old Michael Brown in the St Louis suburb of Ferguson.

Lanier expected body cameras to slash the time spent by supervisors investigating citizens' complaints and discourage individuals from trying to assault a .