SAN FRANCISCO -- Hundreds of demonstrators gathered Tuesday evening in front of San Francisco City Hall in response to the state Supreme Court's ruling upholding Proposition 8, the voter-approved ban on same-sex marriage.

The demonstration, organized by the group Marriage Equality, is scheduled to include a march to the Martin Luther King Jr. monument at Yerba Buena Gardens for a 7 p.m. rally.

Police Sgt. Lyn Tomioka said police will maintain a high profile during the protest, which follows an earlier demonstration in which some 160 people were arrested after blocking an intersection.

Hundreds of people filled Van Ness Avenue at Grove Street late this morning after word spread of the ruling. The court also ruled that roughly 18,000 existing same-sex marriages in California remain valid.

Around 12:45 p.m., officers were seen placing plastic handcuffs on protesters and leading them to police vans waiting nearby. With each new arrest, the crowd cheered.

Tomioka said the protesters were arrested for being outside a crosswalk and failing to obey an officer. Tomioka said she was not aware of any injuries or acts of vandalism related to the protest.

She said 157 adults were arrested, three juveniles were cited and released to the care of their parents, and one demonstrator was taken into custody but then released for medical reasons.

As of mid-afternoon the intersection had been cleared and traffic was moving through normally.

"Today, even though it seems like a really high number (of arrests), it was a peaceful demonstration," Tomioka said.

The state Supreme Court by a 6-1 vote Tuesday upheld Proposition 8, passed by California voters in November. The initiative was approved by 52 percent of voters as an amendment to the state Constitution.

In its ruling, the court rejected three lawsuits in which same-sex couples and local governments claimed the measure could not be passed simply as an initiative because it was a constitutional revision rather than an amendment.