Riot police fired tear gas, pepper spray and flash bombs in downtown Vancouver Wednesday night to try to disperse angry rioters who set cars on fire, looted stores and taunted police officers after the Canucks' 4-0 Stanley Cup final loss to the Boston Bruins.

Police declared the downtown fan zone area near the CBC building and the central post office a riot zone. Anyone not leaving the West Georgia Street area immediately could be arrested, they warned.

Police used batons and also turned police dogs on the rioters, slowly pushing the crowd back along Georgia Street from Hamilton Street to Cambie Street.

Two police cars were set on fire in a parking lot on Cambie Street near one of the areas where police were being confronted by a few dozen people among the hundreds present who were throwing debris at officers.

The riots shook Vancouver residents, and prompted thousands to sign up to a Facebook campaign that aimed to identify rioters and looters. There is also a campaign underway to get people to clean up the city, beginning Thursday morning.

Witnesses were encouraged by Facebook campaign organizers to post pictures of rioters in the act, in the hopes that they might be recognized and identified. More than 20,000 people had joined by the morning Thursday.

"Prosecute the thugs," wrote Lorraine Bennett on the site. "Clearly they hate the Canucks, they hate Vancouver."

'Unfortunately, the tables have turned tonight'

Most people who stayed in the riot areas were watching the confrontation, while a few young men who covered their faces were confronting police.

"You don't ever hope for a situation like this," said Vancouver police Const. Jana McGuinness.

Rioting can carry a life sentence Under Sections 67-68 of the Criminal Code of Canada, a public official may read what's colloquially called the "Riot Act" in order to disperse an unruly crowd: "Her Majesty the Queen charges and commands all persons being assembled immediately to disperse and peaceably to depart to their habitations or to their lawful business on the pain of being guilty of an offence for which, on conviction, they may be sentenced to imprisonment for life." People who do not "peaceably disperse" within 30 minutes are "guilty of an indictable offence and liable to imprisonment for life."

"You celebrate the good times and you prepare for the bad times and that's exactly what we've done. Unfortunately, the tables have turned tonight."

In addition to the riot police, officers were also called in from several neighbouring departments to help control the unruly crowd.

Vancouver fire department Capt. Gabe Roder said it was not clear how many fires had been set. Fire crews were instructed to leave the downtown core by police, and the department made a decision early in the evening to respond to fires only where the public was in danger.

Officials say dozens of people were injured, but most were being treated for tear gas or pepper spray exposure.

Vancouver General Hospital officials said there were two major traumas, three stabbing victims and one head injury.

A spokesperson for St. Paul's Hospital said the emergency room had seen at least 57 people with injuries related to the riot, most of whom were treated for tear gas exposure and released. Others, officials said, were cut with broken glass or had fractured bones. There was one major trauma, officials said, but released no further details.

B.C. Ambulance also confirmed that a man had fallen or jumped off the Dunsmuir Viaduct and was in critical condition in hospital.

Bus transit suspended

A number of cars had also been set alight in a parkade at West Georgia Street and Seymour Street.

Vandals were seen jumping on a pair of police cars in a parking lot on Cambie Street. One of the cars had been turned on its side but later was righted.

TransLink had stopped all bus service to and from the downtown area, but SkyTrains were still running to and from downtown stations.

Vancouver Mayor Gregor Robertson said the situation was "despicable."

"It's absolutely disgraceful and shameful and by no means represents the city of Vancouver," said Robertson. "We've had a great run in the playoffs here, great celebrations, and what's happened tonight is despicable."

"We are dealing with a small number of troublemakers," said the mayor. "They will be held accountable. There's a lot of photographic evidence. We're asking people to keep whatever pictures they're taking… because these people will be held accountable for this."

Cambie Street Bridge was also closed for several hours Wednesday, blocking access to downtown Vancouver.

The second Facebook group called for Vancouver residents to clean up after the riots.

The "Post Riot Clean-Up - Let's help Vancouver" group had more than 11,000 members by the morning.

"I'm living in it so I will definitely be helping," wrote Beverly Akhurst. "I would love to see the people who did this to my home forced to do the cleanup though."

Robynn Mexican-Wonder wrote: "I love this city and will be there to help for sure! I won't trash the people who trashed the place, instead I'll just pick the trash up."

Vancouver police, who were using Twitter throughout the night to get information to the public, said on the micro-site they will let people know Thursday how to post videos and photos of suspects.

Game was winding down

Trouble started in the closing seconds of the game when a thick plume of smoke, believed to be from fireworks, wafted above the crowd on West Georgia Street in front of the central post office building. Moments later, a car burst into flames and fights broke out.

One of the several cars set alight by angry hockey fans in downtown Vancouver Wednesday. (CBC)

The number of arrests is expected to be in the dozens.

Glass windows were broken at the Bank of Montreal on West Georgia and at the Hudson's Bay Company.

Widespread looting was reported at the Bay store, at the downtown London Drugs, Chapters, Sears and Future Shop.

In addition, a fire was reported at a parkade on Seymour Street. Few details were available, but reports indicated several cars were on fire. There were also reports of garbage cans and portable toilets on fire throughout the downtown core.

Some in the large crowd that gathered outside to watch the game on big-screen TVs decided it was prudent to begin leaving early as it looked like the home team was going to lose the game. Many of those taking an early exit were parents with young children, concerned at the threat of over-crowding.

Violence not anticipated

Earlier, before and during the game, fans were packed tight but good-natured as they cheered on their team, which had won at home in every previous game against Boston in this Stanley Cup final series.

Police had consistently used a strategy of engagement with the crowds that had gathered for the previous games. Officers readily exchanged high-fives and good natured banter with fans.

The engagement technique was considered a major success during the 2010 Olympics, when similar numbers of fans flocked to the downtown core.

Police tried to nip the violence in the bud by closing liquor and beer stores early, but it appeared to have no effect.

"We will have to sit down and evaluate exactly what happened here. It's going to be a black mark for a very, very long time," McGuinness said.

The strategy was also part of an effort to avoid a repeat of the 1994 Stanley Cup riot, which occurred in Vancouver's downtown area on June 14 that year, after the Canucks lost in the seventh game of the Stanley Cup final in New York against the Rangers.

It's expected the damage from Wednesday's riot will far exceed that of 17 years ago.