Police are searching for two assailants who sneaked into a backyard party in California on Sunday and opened fire while a small crowd watched football on television, killing four people and injuring six others.

Fresno Police Chief Andrew Hall said the house where a group of Hmong family and friends had gathered was deliberately targeted, but the shooters fired at random once they saw men in the backyard watching football.

Mr Hall said there was no immediate word on a motive and so far there was no indication that any of the victims knew their attackers.

The men who died were ages 21 to 40, he added.

Three were found dead when emergency crews arrived. A fourth person died at a hospital. Six others were hospitalised in critical condition but are expected to survive, authorities said.

Police Deputy Chief Michael Reed speaks to reporters at the scene
Police Deputy Chief Michael Reed speaks to reporters at the scene (Larry Valenzuela/The Fresno Bee via AP/PA)

Mr Hall said police were investigating whether the shooting was connected to a recent disturbance involving some of the people at the party.

He also announced the establishment of an Asian gang task force ahead of the Hmong New Year, out of concern about the possibility of more violence.

California has the nation’s highest population of Hmong, a south-east Asian ethnic minority.

Residents complained that other shootings have happened recently in the same area and Calvin Gatison, who lives on the same street, said it had been peaceful for years, but at least two shootings happened in recent weeks.

It was at least the second fatal gun attack on Sunday in Fresno, the Fresno Bee reported.

A man in his 20s was shot to death at a home in another part of the city. Police have not said whether the incidents could be connected.

Representative Jim Costa, a Democrat who represents the Fresno area in Congress, said he was saddened to hear of another shooting “this time in my own district”.

He said in a statement that “thoughts and prayers are not enough!” and urged the Senate to take up gun-control legislation.