At least three people were killed when a Navy helicopter with five people aboard crashed into the ocean during a training exercise southwest of San Diego, authorities said Wednesday.

Rescue crews recovered three bodies and were continuing the search for the other two crew members, said Lt. Karen Burzynski, spokeswoman for the Navy's 3rd Fleet in San Diego.

"There were five crew members on board and three deaths have been confirmed," Burzynski said.

The HH-60 Seahawk helicopter had taken off from the aircraft carrier USS Nimitz and went down about 11:30 p.m. Tuesday.

Helicopters and boats from the Navy, Coast Guard, San Diego Harbor police, U.S. Customs and Border Protection and Mexican Navy were searching an area near the Coronado Islands off the northwest coast of Mexico for survivors, said Coast Guard Petty Officer Henry Dunphy.

There was no information on a cause, and the names of the crew were being withheld while authorities notify their family.

It wasn't immediately clear if the Seahawk was equipped with a flight data recorder.

Such devices, which record air speed, altitude, pitch and engine power, aren't required in many military aircraft.

The helicopter was part of an anti-submarine squadron from Carrier Air Wing 11. The Nimitz and a half-dozen other ships in its strike group were taking part in the search and rescue training exercises.

The Seahawk is a twin-engine helicopter typically used for anti-submarine warfare, search and rescue, drug interdiction, anti-ship warfare, cargo lift and special operations.

In January 2007, four Navy crew members were killed when another Seahawk helicopter slammed into the Pacific during a training exercise off San Diego.

Naval investigators spent months probing the crash involving the MH-60S Seahawk but couldn't determine its cause because the helicopter did not have a flight data recorder, according to an investigation report obtained by the San Diego Union-Tribune.

As a result of the crash, the investigators urged the Navy to install crash-resistant flight data recorders on its aircraft.

A Navy spokeswoman said facts were still being gathered and declined to answer specific questions about the crash.