OAKLAND — As many as 40 people were arrested in downtown Oakland early Thursday after what was mostly a peaceful day during the general strike Wednesday turned heated.

Late in the evening, protesters temporarily took over a vacant building, started fires in downtown and used homemade bomb launchers to fire M80s at police.

At 1 a.m. police had used tear-gas and flashbang grenades in attempts to clear the crowd from downtown streets. Some protesters tried to calm the situation by chanting “Don’t throw (crap)” and yelling “Stand still the world is watching” but others continued to stand off with police and refused to leave despite police calling an “unlawful assembly” at midnight.

Shortly after 1:30 a.m. police were ready to move in on the Occupy Oakland camp at Frank H. Ogawa Plaza and announced that arrests would be made. At least 100 tents are housing hundreds of people there.

Interim Police Chief Howard Jordan said there are about 70 people “determined to cause trouble and instigate a confrontation with police.” They plan to release their photos at some point. Jordan said officers intended to separate the troublemakers from the rest of the campers. He said around 2 a.m. that between 30 and 40 had been arrested, although he could not confirm the exact number.

They may have been some of the same vandals who trashed Whole Foods on Wednesday.

“We are aware of people bent on causing problems, and we’re taking steps to address those problems,” Jordan said

Police are reporting no injuries to officers, although some protesters were hurt. Witnesses said one man was hit in the leg with a projectile fired by police, and earlier Wednesday, two protesters were struck by a car on their way to a rally at the Port of Oakland. Early reports are false that one of those struck died; all injuries are believed to be nonfatal.

Early in the chaos Mayor Jean Quan asked protesters to call her and gave them her phone number; there was no word on whether Quan had been called by protesters.

The general strike Wednesday, the first one in Oakland since 1946, was mostly calm, peaceful and organized during the day.

Before the sun set Wednesday, more than 4,500 walked from downtown to the port and stretched several blocks down Middle Harbor Road leading into the port as they begin their attempt to shut down operations. About 5 p.m., they successfully shut down the port, said Director Omar Benjamin.

Before the building takeover shortly before midnight Wednesday, Quan said she was happy the crowd — which police estimate hit 7,000 people at one point — protested all day with only a small amount of destruction and violence.

Oakland is being watched worldwide as one of the largest and possibly the most volatile Occupy movements around the globe.

On Oct. 25, 1,000 people marched in the streets, threw bottles and rocks at police and clashed with officers, who launched projectiles and tear-gas into the crowd. A former Marine, Scott Olsen, 24, fell to the ground during the clash and remains hospitalized with a fractured skull; witnesses said he was struck by a tear-gas canister. Quan has since allowed the Occupy movement to rebuild the camp at the plaza and about 100 tents have popped up.

The nighttime clashes followed an early-morning raid on the Occupy Oakland encampment, where police overturned tents, ripped down signs and arrested scores of protesters.

Jordan said Wednesday that the plan had been to facilitate a peaceful march.

“We react to the actions of the crowd. (Wednesday) the crowd has been peaceful, with no threats to police officers, and we allowed them to peacefully assemble. When crowd becomes assaultive or agitated, we’re required by law to respond. That hasn’t happened here. What you saw tonight was minimal presence,” he said.

Quan spokeswoman Sue Piper said city leaders know that the sight of police lines could incite the crowd, and putting fewer police on the streets earlier in the day was deliberate.

But there was a ruckus at 11th Street and Broadway after two people were hit by a motorist.

About 8 p.m., a man and a woman were struck by a car at 11th Street and Broadway. The male driver of a silver Mercedes ran a red light and struck the pair, said Joe Jackson, 37, of Oakland, who witnessed the incident.

Onlookers said the driver deliberately ran over the protesters, and accelerated after a man hit the hood of the car. The windshield was splattered with what appeared to be a milkshake. After the car stopped at the other end of the intersection, the driver switched seats with his female passenger. About 40 people gathered in the intersection and some pulled open the driver’s door.

The woman inside shouted: “I’m sorry, I’m sorry, I’m sorry!” The injured man and woman were taken away in ambulances. Their conditions are not known, but both have non life-threatening injuries. Reports that the one of those struck had died are untrue. Police released the driver.

The general strike was called by Occupy Oakland and supported by residents, a few small businesses, teachers and nurses with the California Nurses Association. It was intended to shut down the city for the day in a rally cry against corporate greed, widespread unemployment and wage inequality.

The worldwide Occupy movement decries the economic wealth of the very rich 1 percent while the remaining 99 percent of the population struggles in the down economy.

Throughout the day, at least five businesses were vandalized, mostly banks and a Whole Foods Market.

At the Whole Foods at 27th and Bay streets, a splinter group wearing black clothing and face masks threw paint balls, left graffiti, tore up a fence and broke a window before the larger crowd turned on them and forced them to stop. About 75 people were inside the store at the time. No injuries were reported.

Joan Bechtel, of Pittsburg, and a friend were inside the grocery when the vandalism started and were held inside the store for 45 minutes.

“People were scared at first, and there was a lot of tension there for quite a while,” Bechtel said. “We heard (the protesters) were coming back and the employees said they had to close the store, and they let us out.”

Oakland City Council President Larry Reid took was not pleased with the destruction.

“Look at Whole Foods. Look at Bank of America and the Kaiser Center. Look at Chase Bank. It’s not even dark yet,” Reid said of the midafternoon destruction.

At Bank of America in downtown Oakland, some protesters pounded on the locked doors, defaced ATMs and broke a window before moving down the street to Wells Fargo.

Several windows were also broken at the Wells Fargo at 12th and Broadway by a splinter group as the majority of demonstrators urged them to stop.

Some bank branches were closed all day, including the Wells and Citibank outlets near Oakland City Center.

There were also some unhappy truckers at the port when the protesters blocked the roadways.

“To me this is all (baloney),” said Sam, who declined to give his last name, but said he is a hauler for NevCal Trucking out of Reno and picked up a container at PortsAmerica terminal Wednesday afternoon. When he tried to leave, the exit gate manned by U.S. Customs and Border Protection had closed early because of the impending protest.

“These people are out here trying to make a living. I get paid per run, I don’t get paid by the hour,” he said. “My personal opinion? The 1 percent down here is protesting, the 99 percent is down here working.”

At least 200 city workers took Wednesday off, about 5 percent of the city’s entire workforce. Other city and port workers were sent home early as the crowd of demonstrators swelled to about 5,000 downtown.

For much of the afternoon the large crowd split off into separate marches, with some staying at the Occupy Oakland camp at Frank H. Ogawa Plaza and participating in teach-ins and sit-ins, and others marching and protesting.

At the plaza, members of the Alameda Labor Council served free hot dogs, hamburgers, veggie dogs and veggie burgers to a ravenous crowd and had given away more than 4,000 meals. Firefighters from the City of Alameda with Alameda Local 689 worked the massive charcoal grills while other volunteers began picking up the mountains of trash overflowing from garbage bins.

“It’s been exciting. There’s been great energy all day,” said Josie Camacho, secretary-treasurer of the Alameda Labor Council.

Also on Wednesday, a crowd of more than 300 parents with babies, toddlers and children of all ages marched from the main branch of the Oakland Public Library to 13th and Broadway as part of a “children’s brigade.” Children led the march and chanted “Who are the 99? We are the 99!” while parents with wagons, strollers and infants in carriers marched behind them, toting snacks, crayons, chalk and bubbles.

“I’m only 6. I can’t afford a lobbyist” read one sign.

Chris Specker, a Temescal resident who owns the “It’s Your Move” game store on Telegraph Avenue, attended the march with her 5-year-old daughter Sarah, who is in kindergarten at Oakland Unified’s Peralta Elementary. Specker said she was one of several Peralta parents who signed her daughter out of school at lunch time Wednesday.

“The concept is easy: everyone needs to share,” said Specker, a single mom. “I closed my store to support the strike, and I want my daughter to learn that activism is important.”

Specker said she hoped that Oakland residents will support local businesses and she planned to eat dinner with friends at a downtown restaurant before heading home.

Students and teachers from Berkeley and Laney colleges also marched downtown to join the strike after first stopping to serve a symbolic “eviction notice” at Oakland Unified School District headquarters.

Joel Velasquez, a parent of two children at Westlake school, said school board members are “on notice that they will be evicted from office in the next election for doing the dirty work of the 1 percent.”

“They are part of institutional problems that cause hardship on low-income children,” Velasquez said.

Several businesses, including Tullys, the Men’s Wearhouse and the Grand Lake Theater, closed to support the general strike to protest the inequality of wealth and power.

The UC Office of the President kept its more than 800 employees home over concerns that BART might be shut down at some point. About 1,300 people affiliated with UC work in the building, and all stayed away.

Sam K., owner of Jimmy’s Deli said he decided to keep his delicatessen on Broadway closed all day.

“What can you do? We have to close,” said Sam, who asked that his last name not be used. “Our regular customers don’t want to come down here while this is going on,” he said, gesturing to the demonstrators who had filled Broadway.

“It’s getting to be too much to run a business in Oakland,” Sam said.

Oaklandish, a T-shirt and accessories retailer, kept its doors closed.

“We wanted to show our solidarity with Occupy Oakland,” said Angela Tsay, owner of Oaklandish. Her store opened in July on Broadway.

Oaklandish printed free T-shirts that said “Working for Oakland 99 percent.” Tsay also arranged for a disc jockey to play music in front of the shuttered store and paid her dozen employees for the day, despite the store being closed.

Staff writers Dana Hull, Matt O’Brien, Angela Woodall, Paul T. Rosynsky, George Avalos, Thomas Peele, Josh Richman, Robert Salonga, Hannah Dreier, Katy Murphy, and Scott Johnson contributed to this story.