Rowdy crowds took to the streets of Los Angeles after the Dodgers won the World Series, setting a city bus on fire, breaking into stores and lighting off fireworks.

A dozen arrests were reported by police on Thursday, but officials emphasised that most fans celebrated peacefully.

Video showed revellers throwing objects at police in downtown LA as sirens blared and officers told them to leave the area late on Wednesday after the Dodgers defeated the Yankees in Game 5 in New York.

Other video showed someone standing atop a bus waving a Dodgers banner and people running from a boarded-up Nike store with armfuls of sneakers before throwing the merchandise into cars parked outside. No injuries were reported.

Despite some unrest, "the overwhelming majority of celebrations last night were joyful and peaceful," Mayor Karen Bass said at a Thursday news conference, discussing the logistics of Friday's planned victory parade.

"We will work to keep Angelenos safe as always," Bass said, emphasising that "violence of any kind will not be tolerated."

Officials said the Los Angeles Police Department will be on high alert throughout the week to protect communities and businesses in the city, which has been the site of previous unrest after championship wins by both the NBA's Lakers and the Dodgers.

There were some "unruly, and at times violent and hostile celebrations" after Wednesday's win, with several acts of vandalism, including the burning of a Metropolitan Transportation Authority bus, LAPD spokesperson Officer Drake Madison said.

Arrests were on charges such as failure to disperse, receiving stolen property or commercial burglary.

There were also several instances of street takeovers downtown and police used less-lethal munitions to control several hostile and violent crowds.

The Dodgers plan to commemorate their championship on Friday with a downtown parade followed by a celebration at Dodger Stadium.