The Federal Aviation Administration identified the planes as a single-engine Cessna 152 and a twin-engine Cessna 340, noting that one person was aboard the Cessna 152 and two others were riding in the Cessna 340.
No one on the ground sustained any injuries as a result. Reports have suggested at least two individuals involved in the accident were killed.
"Multiple agencies responded to Watsonville Municipal Airport after 2 planes attempting to land collided. We have reports of multiple fatalities," the city said in an earlier tweet on Thursday. It stated that the incident took place at about 3 p.m. local time.
Citing law enforcement officials, local media reported that the mid-air collision saw one of the planes crash into a building at the airport, while the second aircraft crashed next to the airport, at a nearby intersection.
An investigation by the FAA is ongoing.