Two children were killed and two adults were left in critical condition after a small plane crashed near the Sierra Sky Park Airport in the city of Fresno, in the western US state of California, on Saturday afternoon, authorities said.

Fresno sits in California's Central Valley, roughly midway between San Francisco and Los Angeles.

The Fresno County Sheriff's Office said the aircraft, carrying four people, went down near the San Joaquin River just before 2 p.m. local time, close to the 7300 block of North Blythe Avenue. Some reports identified the aircraft as a single-engine Grumman American Aviation Corp. AA-5.

Tony Botti, a public information officer for the sheriff's office, said deputies, Fresno firefighters, and police officers responded to the scene after receiving a call around 1:50 p.m. Emergency crews found the wreckage on fire atop a bluff near the river, with flames spreading into the nearby dry brush.

Firefighters were able to extinguish the fire before it reached nearby homes, the sheriff's office said. Two adults were transported to Community Regional Medical Center in critical condition. The identities and ages of the victims, along with the relationship between the four occupants, had not been confirmed as of Saturday evening.

The cause of the crash remained under investigation. The Federal Aviation Administration (FAA) and the National Transportation Safety Board (NTSB) are both involved, with the NTSB leading the inquiry into what went wrong, Botti said. A perimeter was set up around the crash site to preserve it for investigators.

The Fresno Police Department, Fresno Fire Department, Fresno County Sheriff's Office, PG&E, and North Central Fire Department all responded to the scene, according to broadcaster ABC30. The crash also briefly knocked out power for nearby residents; PG&E later confirmed service had been restored.

Sources: ABC7 News/NBC Bay Area