A small plane crashed into a commercial building in the US state of California on Thursday, killing at least two people and injuring 18 others, police said.

The crash took place early in the afternoon near Fullerton Municipal Airport, 40 kilometres southeast of Los Angeles. The cause remains unknown.

“There are two confirmed fatalities,” Fullerton police said on X. Additionally, 10 people were hospitalised and eight others were treated at the scene.

Investigators do not yet know if the deceased were plane passengers or if they were workers at the building where it crashed, a police officer told local station KTLA.

Television footage showed a gaping hole in the roof of the building, with smoke pouring out.

“All we hear is like a loud noise, boom, and that’s it. Then we started running out” of the building, Jerome Cruz, one of the workers who witnessed the scene, told CBS News.

The plane was a single-engine Van’s RV-10, a small model with four seats, according to the Federal Aviation Administration, which has opened an investigation.

Another crash near Fullerton Airport injured two people in November.

Friday’s incident follows a series of aviation disasters last week. On December 29, at least 179 people were killed when an airliner belly-landed and veered off the runway, erupting in a fireball as it slammed into a wall at South Korea’s Muan International Airport.

It was the worst air accident involving a South Korean airline in nearly three decades and on track to become the country’s deadliest ever, according to ministry data.

On the same day, a passenger plane flying from Norway to the Netherlands went off the runway during an emergency landing.

“Flight #KL1204, a Boeing 737-800, veered off the right side of runway 18 after landing at Oslo Torp Sandefjord Airport. The flight diverted there shortly after takeoff from Oslo Airport (OSL),” according to a statement issued by Royal Dutch Airlines and posted on X.

It said 176 passengers and six crew members on board were not harmed, while an investigation has been launched into the incident.

Meanwhile, an Air Canada flight was forced to make an emergency landing at Halifax Stanfield International Airport after experiencing a malfunction with its landing gear on the night of December 28.

Air Canada Flight 2259, departing from St. John’s International Airport, experienced landing troubles at 0130GMT that caused skidding and an engine fire, prompting a swift response from emergency crews to ensure the safety of all onboard, several media outlets reported.