One airplane was apparently flying low or had just landed when it crashed into the other plane around 8:30 a.m., said Scott Gaenicke, public information officer for Titusville Fire and Emergency Medical Services.
FAA spokesman Warren Woodberry said the plane on the ground appeared to have been taxiing to a ramp area. Two people who were in that plane were killed, Gaenicke said.
The other plane cartwheeled for about 100 yards before landing belly-up on a grass median at the airport, Gaenicke said. Bystanders aided two people who were in that plane, which also caught fire, he said.
"It's kind of shocking," he said. "It's certainly devastating to see."
Gaenicke said one of the survivors was in "grave" condition and the other was in extremely critical condition.
Woodberry said one of the aircraft was classified as an experimental aircraft.
The Arthur Dunn Airpark at Titusville, just west of the John F. Kennedy Space Center, was closed. FAA and National Transportation Safety Board inspectors were en route.