Police have arrested more than 150 protesters near a convention center where thousands of biotechnology scientists and entrepreneurs are meeting.

About 200 demonstrators protested on the sidewalks early Tuesday, though they failed to shut down the annual Biotechnology Industry Organization (search) convention as they had vowed.

They did cause disruptions in traffic, however, and heckled attendees as they attempted to enter the Moscone Convention Center (search).

"Arrest them, shoot them," protesters shouted as police escorted attendees across a barricaded street.

Police wouldn't say how many officers were at the scene, but it appeared their number equaled that of the protesters. Police also wouldn't estimate the number of protesters.

After a lull Tuesday afternoon, about 150 protesters again gathered in the evening and occupied an intersection on one of this city's main thoroughfares, again snarling traffic.

Officers who had remained in the area surrounded them and arrested about 125 people who would not disperse. That came after 33 people were arrested earlier in the day, according to police spokesman Dewayne Tully.

Some demonstrators said police moved in without any warning.

Many of the morning protesters, such as Kamala Stuart, 53, of Oakland, were demonstrating against genetically modified food.

"They should label the food, if they think it's so good," she said in the morning. "We want people to know, to question this stuff."

Conference organizers said most attendees were affiliated with the pharmaceutical industry.

"This is a protest rooted in ignorance," said Jeffrey Feldman, a merchant banker from Philadelphia attending the conference.

An estimated 18,000 biotechnology scientists, executives and government officials are in town for the convention. They were joined by prominent federal officials, as well as governors from states which tout themselves as biotech friendly.

A group calling itself Reclaim the Commons (search) had promised to prevent attendees from entering the convention center Tuesday, the same day the San Francisco Board of Supervisors is scheduled to consider a resolution praising demonstrations against the biotech industry.

Police said they arrested protesters who blocked traffic. About 12 protesters were arrested when they carried out what they called "guerrilla gardening" in an intersection in front of the convention center. Surrounding some potted plants, they linked themselves by grasping chains covered with plastic pipes.

At another intersection nearby, about 50 bicyclists were blocking traffic, police said.

Like many protests in San Francisco, this one had its festive moments. At the center, a group of protesters clapped and danced as one man played the flute.

The protesters seemed to represent a spectrum of views. Some pushed conference attendees aside and shouted profanities. Others stood peacefully out of the way.

"I'm not here to stop people, to block people," said Connie Chuang, 27, of San Rafael. "I'm here to be a body, be a conscience."