Both planes were single-engine craft known as "experimental" or amateur-built, officials said. The Experimental Aircraft Association Chapter 866 was hosting a pancake breakfast at the airport, the Arthur Dunn Airpark.
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.
Gaenicke said the plane on the ground appeared to be taxiing to a ramp area when it was hit. 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, Gaenicke said. Bystanders aided two people in that plane, he said.
"It's kind of shocking," he said. "It's certainly devastating to see."
A member of the Experimental Aircraft Association, Larry Gilbert, said the pilot of the plane that was landing appeared to lose control and was trying to take off again when it slammed into the other plane.
The two injured people were taken to Orlando Regional Medical Center with severe burns. Gaenicke said one was in "grave" condition and the other was in extremely critical condition.
Gaenicke said both planes are considered experimental aircraft.
"They're not like your off-the-shelf, already pre-manufactured (aircraft)," Gaenicke said. "These are home-built type aircraft that one would buy as a kit and put together."
It was difficult to determine the exact models of both planes, Gilbert said. "They were so totally destroyed."
The airfield doesn't have a control tower, the Federal Aviation Administration said.
One plane was registered to Christen Air Inc. in Wilmington, Del., according to the FAA's online aircraft registry. A telephone listing for that company was not immediately found.
The other was registered to William E. Hess of Daytona Beach, according to FAA records.
The airpark at Titusville, just west of the John F. Kennedy Space Center, was closed. FAA investigators were on the scene and National Transportation Safety Board inspectors were expected to arrive later Saturday.