Police arrested a man on suspicion of murder after a driver plowed into crowds at the Venice Beach boardwalk, a seemingly intentional hit-and-run that killed an Italian woman on her honeymoon and injured 11 others.

Nathan Louis Campbell, 38, of Los Angeles, was arrested after he walked into a police station in neighboring Santa Monica about two hours after the incident and told police that he was involved.

Campbell remained jailed Sunday on $1 million bail.

Deputy Chief Kirk Albanese declined to discuss a motive but said there was no indication that the attack was a terrorist act or that anyone else was involved.

Security video taken at the popular tourist site showed a man parking a black car, stepping out and surveying the leisurely scene for several minutes before getting back into the vehicle and speeding into the crowd. Hundreds of people who had been walking or sitting at cafes raced to get out of the way before the vehicle sped out of sight.

A witness reported 'blocks and blocks of people just strewn across the sidewalk' after a car rammed into beachgoers. (Alex Thompson/Associated Press/Venice311.org)

Witnesses reported a horrifying aftermath.

People were "stumbling around, blood dripping down their legs, looking confused not knowing what had happened, people screaming," said Louisa Hodge, who described "blocks and blocks of people just strewn across the sidewalk."

The Italian woman was identified as Alice Gruppioni, 32. Her family in Bologna told the Italian news agency LaPresse that she had been on her honeymoon after a July 20 wedding.

Gruppioni worked as a manager for the family business Sira group, which makes radiators. Her father, Valerio Gruppioni, runs the company and was formerly president of the Bologna soccer team, according to LaPresse.

The family declined to speak to The Associated Press on Sunday.

Authorities said another person was critically injured. Two others were taken to hospitals in serious condition and eight suffered less serious injuries.

The crash was not far from where an elderly driver sped through an open-air farmer's market in Santa Monica in 2003, killing 10 people and injuring more than 70 others.

Investigators said George Weller, who was 86 at the time, mistakenly stepped on the gas instead of the brake and then panicked. He was doing up to 96 kph when he plowed through the market. Weller was convicted of 10 counts of vehicular manslaughter with gross negligence and was sentenced to probation.

'Tons of people out'

It was not immediately clear how fast the car in Saturday's crash was going.

According to security video and witness accounts, the driver parked next to the Cadillac Hotel and twice walked out to the boardwalk before getting into the Dodge Avenger and accelerating, swerving around yellow poles meant to prevent cars from getting into the pedestrian-only area and onto the boardwalk.

"I heard a big 'boom, boom,' like the sound of someone going up and down the curb, it was super loud," said Alex Hagan, 22, who was working the desk at the Cadillac Hotel and watched the scene unfold from the start.

The driver knocked over two mannequins and then started hitting people, swerving from side to side and often running straight into them.

Video showed the car hitting at least three vendors who were sitting at their sales booths.

Pedestrians gather as police and fire officials inspect the scene of the incident on the Venice Beach boardwalk. (Maarten Smitskamp/Associated)

Two women who appeared to be in their 60s were also struck, Hagan said.

Many people ran after the car, screaming and cursing as it sped away, he said.

Golestan Alipour, bartender at Candle Cafe & Grill, said the large sedan carefully maneuvered between a storefront and metal poles that had been erected to prevent anyone from driving onto the boardwalk. A free-standing ATM barely slowed his race toward the crowds.

"The restaurant was full. Everybody ran," Alipour said.

The car went on for several blocks, knocking down a fortune teller who had a table, a couple selling jewelry and a woman who does tattooing, Alipour said.

Authorities at the scene searched for evidence across the boardwalk, which is in a part of Los Angeles known for eccentricities. The 2.4-kilometre ribbon of asphalt that runs along the sand a few hundred yards from the ocean is home to galleries, restaurants, tattoo shops, skateboard parks and the famous outdoor weight room known as Muscle Beach. It can draw as many as 150,000 people on summer weekends.

Police found a car nearby that they believe belonged to the driver, he said.

Hodge said she and her friend, Ashley Taylor, had made note of the large number of people walking along the seaside.

"It was a really nice day. There were tons of people out. In fact, we were talking about how packed it was, because we were having a hard time getting through all the people," Hodge said.

The two women stopped to buy ice cream and a couple of hats, which may have saved their lives. They stepped out of a store to see the aftermath, as emergency crews arrived and started putting victims on tarps.

Hodge saw one man and woman lying next to each other, wearing head braces, barely able to move.

"They were just laying next to each other and grasping hands," Hodge said, "just a man and a woman holding hands."