The crash took place at Watsonville Municipal Airport on California's central coast just prior to 3:00 p.m. as the planes collided while both were attempting to land, according to Michelle Pulido, a spokeswoman for the city of Watsonville.
Pulido said the exact number of deaths wasn't immediately clear during an update on Thursday.
The two planes, described as a twin-engine Cessna 340 with two people on board and a single-engine Cessna 152 carrying one person, were on their final approaches at the time of the collision, according to a statement from the Federal Aviation Administration obtained by NBC News.
The City of Watsonville's Twitter account shared a photo depicting what appeared to be destruction at the airport.
Watsonville officials said the cause of the crash wasn't immediately clear and an investigation is ongoing.
"We are absolutely saddened to hear about the tragic incident that took the lives of several people," the city said in a statement to the community shared on its Twitter account. "The City of Watsonville sends its deepest condolences to the friends and family of those who passed."
The National Transportation Safety Board has also launched an investigation into the collision.