Anti-Trump protests balloon in downtown Oakland, S.F.

Thousands of people took to the streets of San Francisco and Oakland on Wednesday night to protest Donald Trump’s election to the presidency, joining Americans in other U.S. cities who vented their frustration with Tuesday’s race results at a string of swiftly organized rallies.

A gathering of a few hundred at San Francisco’s Powell and Market streets quickly swelled to several thousand as a sea of demonstrators emerged downtown before veering toward the Mission District with signs reading “Stop Trump” and “Impeach.” The crowd roared with such slogans as “People united will never be divided,” in reference to the Republican’s divisive comments — often construed as sexist and racist — during the heated campaign.

While Californians cast nearly twice as many votes for Democrat Hillary Clinton as the billionaire developer and reality star, the state’s 55 electoral votes were not enough to derail Trump’s unexpected path to victory.

San Francisco resident Kevin Wiggins, 24, who marched down Market Street, said the prospect of a Trump presidency is especially troubling because of his apparent lack of concern about police brutality.

“I don’t want to see what he’s going to do to the country, especially people of color,” said Wiggins, who is black.

A protester fans the flames of a fire during anti Donald Trump protest march in Oakland, Calif., on Wednesday, November 9, 2016. A protester fans the flames of a fire during anti Donald Trump protest march in Oakland, Calif., on Wednesday, November 9, 2016. Photo: Scott Strazzante, The Chronicle Photo: Scott Strazzante, The Chronicle Image 1 of / 29 Caption Close Anti-Trump protests balloon in downtown Oakland, S.F. 1 / 29 Back to Gallery

As the marchers ventured into the Mission District, a couple of college students and friends zeroed in on the issue of the Dakota Access Pipeline and the national debate over oil and harmful fossil fuel emissions.

With Trump pledging to drop a number of federal environmental protections, such as restrictions on fracking enacted under the Obama administration, Foothill Community College student Aaron Grulich of Redwood City said he is worried about the regulation unraveling.

“We don’t know what’s going to happen, but we anticipate it’s going to carry forward, and it could get worse. Who knows?” he said.

Scores of police officers, many in riot gear, helped divert traffic around the San Francisco march, which, after causing congestion along Market, triggered minor backups in parts of the Mission District. No major problems were immediately reported.

In Oakland, police issued an order for protestors downtown to disperse around 8 p.m. after a rally at Frank H. Ogawa Plaza morphed into a march of several thousand people on Broadway and surrounding streets. There were minor scuffles between officers and protestors, and reports of tear gas being deployed by police. The reports were not confirmed. As the evening wore on, some demonstrators were seen lighting small fires and smashing windows of businesses.

During demonstrations earlier Wednesday, immediately following the election verdict, a 20-year-old woman was struck by an sport utility vehicle and seriously injured as she and a couple hundred people spilled onto Highway 24 near Telegraph Avenue along the Oakland-Berkeley border.

The day’s protests, which included a smaller event on Telegraph Avenue in Berkeley, followed calls on social media, often with the hashtag “#NotMyPresident,” beckoning those averse to Trump’s presidential agenda and unhappy with what they see as his record of bigotry. At each of the events, passersby joined in.

“I need to feel community and connection and a safe space to express our rage,” said Oakland resident Gala King, 39, who brought one of her two sons to the peaceful rally at Frank H. Ogawa Plaza.

Like many, King said that her family was shocked that a candidate with plans to build a wall on the Mexican border and put checks on Muslims was elected to the nation’s highest office.

“My son keeps asking me, ‘Did he really win? How could someone so mean be president?’” she said. “It’s really hard to explain how it’s possible.”

Oscar Vivanco, 42, brought his 4-year-old son, Coltrane, who suffers from a rare brain condition and uses a wheelchair, to the Oakland demonstration. He fears his family could lose health benefits that came during the Obama administration as Trump has vowed to eliminate the president’s signature Affordable Care Act.

“We don’t know what to expect, what will be taken away that we’ve taken for granted,” Vivanco said.

Many at the Oakland protest, which was co-hosted by groups Socialist Alternative and Anti-Police Terror Project, said the Democratic Party deserved some of the blame for the Trump presidency. They said the party failed to offer a candidate outside the status quo who could connect with Americans. Several had supported populist candidate Bernie Sanders in the primary.

Oakland Mayor Libby Schaaf issued a statement earlier in the day encouraging residents to channel their frustrations into volunteer work promoting social justice.

“I ask Oaklanders to not just get mad, get involved,” she said.

On Wednesday afternoon, students at several Bay Area high schools, including Oakland’s Technical and Bishop O’Dowd and Berkeley High, walked out of class in protest of Trump’s win.

Demonstrators angry about the presidential race also marched in several cities across the nation, including New York, Philadelphia, Chicago, Los Angeles, Portland and Seattle.

Clinton, in her concession speech early Wednesday, asked her supporters to accept the election results and give Trump a shot.

“We owe him an open mind and a chance to lead,” she said.

J.K. Dineen contributed to this report.

Kimberly Veklerov, Michael Bodley, Jenna Lyons and Kurtis Alexander are San Francisco Chronicle staff writers. Email: kveklerov@sfchronicle.com, mbodley@sfchronicle.com, jlyons@sfchronicle.com, kalexander@sfchronicle.com Twitter: @KVeklerov, @michael_bodley @JennaJourno @kurtisalexander