Los Angeles, Nov 18 (IANS): At least four people were killed and six others injured in a mass shooting by "unknown suspects" who remain at large in California's Fresno city, police said.

Fresno police said that 10 people were shot on Sunday night in the backyard of a house on the 5300 block of East Lamona Avenue near Caesar Avenue, reports The Fresno Bee.

Fresno Police Lieutenant Bill Dooley said it was a "mass casualty incident".

"Officers arrived on scene... What we found were several individuals deceased in the backyard." he said.

Dooley said that "unknown suspects" "snuck" into the backyard and opened fire and then fled the scene.

"What we do know is that this was a gathering, a family and friend gathering in the backyard," he said. "Everyone was watching football when unknown suspects approached the residence, snuck into the backyard and opened fire."

This was at least the second fatal gun attack on Sunday in Fresno. A man in his 20s was shot dead earlier in the day at a home.

The police has not said if the two shooting incidents were related.