Police say the crash happened just before 3am (local time) on Thursday, when Spence's Ferrari crossed a median into oncoming traffic and flipped over several times, ejecting Spence, who wasn't wearing a seatbelt, police said.

Spence was taken to a hospital and placed in the intensive care unit.

"His injuries are not life-threatening. His parents are with him at the hospital," Tim Smith, a spokesman for Spence's promoter, Premier Boxing Champions, told The Associated Press.

Police said they're still investigating the cause of the crash, but they noted that the Ferrari was speeding at the time.

Last month, the 2012 US Olympian added the WBC welterweight title to his IBF strap with a thrilling split-decision victory over Shawn Porter in Los Angeles.

With his rangy athleticism and virtuosic skill, Spence, who is 26-0 with 21 knockouts, has captured fans with a series of crisp victories in recent years.

He won the IBF title in 2017 by stopping Kell Brook in England, and he defended it three times, culminating in a one-sided thrashing of undersized Mikey Garcia in March.

Spence, 29, emerged victorious from his bout with the veteran brawler Porter (30-3-1), which featured several wild exchanges and had the Staples Center crowd of 16,702 on its feet throughout the 12th round and roaring for both fighters when they embraced after the final bell.

Heading into the fight in which he was a heavy favourite, Spence had a lot of attractive options ahead, including a possible fight with the resurgent Manny Pacquiao and a potential bout with fellow unbeaten champion Terrence Crawford after that.

Australian Associated Press