Chris Gade, who lives in the neighborhood, said he heard noise from the party and then gunshots and saw people "screaming and fleeing down the hill".
Airbnb spokesman Ben Breit said in an email that the home's Airbnb ad included prohibitions on parties, weapons, smoking and marijuana use.
Authorities initially reported that four people were wounded but the Contra Costa County Sheriff's Office said later that the exact number of wounded victims was unknown because some of those injured went on their own to hospitals.
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Gunfire erupted at a residence in the Lucille Way and Knickerbocker area just before 11 p.m.
Photos and video taken by reporters at the scene shown paramedics and police in attendance. Several of the partygoers who were injured remain hospitalized, and at least one is in serious condition. Video from the scene showed multiple patients being loaded into ambulances as others limped away from the scene.
The home where the party was held is in a neighborhood of multimillion-dollar homes. The incident happened late Thursday night at an Airbnb rental home in the city of Orinda. City officials had regulated the industry with an ordinance and a registry.
"It's a very somber day here in Orinda", Miller said.