A group of demonstrators caused the shutdown of one direction of the San Francisco-Oakland Bay Bridge in a police-brutality protest tied to the Martin Luther King Jr. holiday.

Members of the group stopped vehicles in all the westbound lanes at about 4 p.m. Monday. They chained themselves and the cars together to form a line across the bridge and laid signs reading "BLACK HEALTH MATTERS" across the roadway.

Traffic was blocked for travelers heading into San Francisco from the East Bay as the holiday weekend was ending.

About 30 minutes later, California Highway Patrol officers were pulling about a dozen protesters from cars and pulling their cars to the side of the road. Traffic soon began slowly moving again.

Mia Birdsong, a spokeswoman for the protesters, tells the San Francisco Chronicle they were from a group called Black.Seed, an offshoot of the Black Lives Matter movement.