Three people suffered minor injuries, police spokeswoman Debra Brown said, adding the driver was arrested for investigation of assault.

Demonstrators surrounded the car and started beating on the vehicle after it hit the marchers, she added.

Five other people were arrested for possible weapons violations and one person was arrested for obstructing, Brown said.

Seattle police would not give an official estimate of Monday's crowd, but organizers anticipated more than 20,000, said Ricardo Ortega of the Comite Pro-Amnistia General y Justicia Social.

Elsewhere in Washington, rallies drew a total of at least 10,000 people in Yakima and Pasco.

"Elite politicians ... have awakened a sleeping giant," King County Councilman Larry Gossett told an evening rally at Seattle's downtown Federal Building. "Everybody, we're all united in this effort to get comprehensive immigrant rights."

An April 10 immigration rights march and rally drew 15,000 people in Seattle.

Thousands - mostly Hispanics - participated in rallies and marches across the country, but some activists in Seattle stressed that immigration issues affect everyone.

Seattle demonstrators waved large American flags and signs that read "Stop the war! Open the borders" and "Equal Rights (not) Special Rights."

Couples walked arm-in-arm beside teenagers and mothers who maneuvered baby strollers through the throng that at one point stretched more that eight city blocks.

Spanish teacher Marta Buell, 36, of Seattle, came to the United States 12 years ago from Mexico. She received her citizenship in 2001.

While the process was easy for her, she said, some of her friends have been deported.

"I've seen how the families get broken up and the kids suffer," Buell said.

She called on Congress to find realistic and compassionate immigration solutions.

"In the end we are humans. We are one," she said.

Monday's nationwide demonstrations and boycotts were organized by immigrant activists angered by proposed federal legislation that would criminalize illegal immigrants and fortify the U.S-Mexico border. The goal was to raise awareness about immigrants' economic power.

In Yakima, police estimated the crowd at 5,000 to 8,000, while organizers placed the number at closer to 15,000. In Pasco's Volunteer Park, the crowd, estimated at about 5,000, arrived by bus and bicycle, on foot and in cars decorated with fluttering U.S. and Mexican flags.

David Gutierrez of Yakima, who helped organize previous immigration rallies, told the crowd at Yakima's Miller Park they had outdone themselves by turning out in such large numbers.

"Not even in the time of Cesar Chavez, may he rest in peace, did this many people come out in the Yakima Valley. Some people don't want us here but we're staying. The economy depends on us," Gutierrez said. The late Chavez, co-founder of the United Farm Workers, led a march of 700 people in the Lower Valley in 1986.

The Pew Hispanic Center, a research organization in Washington, D.C., estimates there are as many as 12 million illegal immigrants in the United States, though other organizations put the number at 11 million. More than 210,000 undocumented immigrants live in Washington, according to the center.

"We're all immigrants in this country. It's not just about the people who just came here recently," said marcher Rebecca Chan, 31, of Seattle, a board member of the Seattle chapter of the Organization of Chinese Americans.

Michael Blanton, 46, a lawyer from Olympia who works with Social Security issues, said he was happy to see the Seattle crowd included whites as well as people of color.

"I just think if people want to come here and do jobs a lot of Americans don't want to do ... more power to 'em," Blanton said.

"This is really about all of our rights and not just about immigrants who are here. It's a debate about what America is going to be," Pramila Jayapal, founder and executive director of Hate Free Zone Washington, said before the Seattle march began.

Much of the debate around immigration has focused on legalization of undocumented workers, but Jayapal said comprehensive immigration reform also must address family reunification, civil and human rights and better worker protections.

Jayapal, who at 16 came to the United States from India 20 years ago to attend school, chided a system where families often must wait an average of 10 years to bring a relative into the country.

"We're still operating with a system that acts like we don't need to bring in additional workers," she said, citing a number of U.S. Labor Department studies that estimate the country's worker shortage at about 500,000.

Monday's demonstrations included economic protests and boycotts of work, school and shopping to show immigrants' importance to the country.

Tyson Foods' meatpacking plant in Pasco was one of about a dozen of the company's plants shut down in part because of Monday's rallies. Most of the company's more than 100 plants were operating as usual, however.

"We have not encouraged workers to join the rallies although we certainly understand the sentiment behind them," said Gary Mickelson, spokesman for Tyson Foods in Springdale, Ark.

At La Tarasca restaurant in Centralia, about 25 miles south of Olympia, owner Manuel Ayala said he was turning away customers Monday after his five workers told him Sunday night that they weren't going to show up.

He said he had mixed feelings about Monday's protest.

"They need opportunities to make a living here. The law affects these people," he said, but said he also worried how the closure would affect his restaurant, which he runs with his family.

"This is a small business," he said. "I'm losing money. What I can I do?"