(CNN) -- — A throng of rescue workers scoured the coastal Florida waters overnight looking for two people missing from an air ambulance crash.
Authorities have already found the bodies of two others in the Atlantic Ocean, a U.S. Coast Guard spokesman said. The four passengers -- two pilots, a doctor and a nurse -- had just dropped off a patient at Fort Lauderdale-Hollywood International Airport and was headed back to Mexico, an airport spokesman said.
A distress call from one of the pilots came just moments after takeoff. An air traffic controller asked him to turn left and keep a certain altitude.
"Not possible," the pilot responded.
The pilot asked to turn around. Seconds later, the pilot said: "Mayday, mayday, mayday."
Coast Guard Petty Officer Mark Barney said the bodies of a man and woman were located just off the coast of Fort Lauderdale.
The two medical staff members worked for Air Evac International, said Albert Carson, the company's director of operations. The pilots worked for a chartered company. Carson said it was not immediately clear who was killed and who was still missing.
"We're waiting on pins and needles ... waiting for more information," Carson said late Tuesday night.
The Learjet 35 plane, which can carry up to eight passengers, was headed to Cozumel, Mexico, officials said.
The cause of the crash was not clear. The National Transportation Safety Board is investigating.
CNN's Dave Alsup and Steve Almasy contributed to this report.