Two men were shot and wounded in the parking lot of Candlestick Park after a preseason football game between the San Francisco 49ers and the Oakland Raiders, and a third man was beaten unconscious inside the stadium, police said on Sunday.

A 24-year-old man was taken to hospital with life-threatening injuries from the shooting on Saturday night, while the other man, in his 20s, was hospitalized with less serious injuries, San Francisco police said.

Police said they had no suspect in custody from the outbreak of violence in the parking lot of San Francisco's Candlestick Park, and that it was not immediately clear if any of the men who were shot were fans of any particular team.

The two men were found in different locations outside the stadium, and investigators were initially unsure if those two attacks were related, San Francisco police spokesman Sergeant Michael Andraychak said.

During the game, a 26-year-old man was beaten unconscious in an upper-level bathroom at the stadium, and was also hospitalized with life-threatening injuries, Andraychak said.

Police said they have not arrested a suspect in the bathroom beating.

San Francisco Mayor Ed Lee and Oakland Mayor Jean Quan issued a joint statement about the violence.

The incidents at Candlestick Park last night after the San Francisco 49ers versus Oakland Raiders game are completely unacceptable, and will be prosecuted to the fullest extent of the law, they said.

The shootings and beating come less than five months after a San Francisco Giants baseball fan was severely assaulted outside Dodger Stadium in Los Angeles, sparking outrage in the city and causing some to question security arrangements at the stadium.

In the Bay area preseason showdown between the San Francisco 49ers and the Oakland Raiders on Saturday night, the 49ers won 17-3.

Andraychak said the violence at Candlestick Park was unusual, and that more often police and security there deal with relatively minor problems, such as public intoxication or use of profanity.

The National Football League, which is trying win back fans after a bitter labor dispute, threatened to delay the upcoming season, condemned the violence.

We deplore the activities of a handful of fans at last night's game and pledge our full support to Mayors Lee and Quan and to state and local law enforcement agencies, a statement from the NFL said. We are carefully reviewing the events to make sure we have a full understanding of the facts.