About 150 turtles have crawled onto the tarmac at New York's Kennedy airport in search of beaches to lay their eggs, delaying dozens of flights.

The slow-motion stampede began last night NZ Time, and within three hours there were so many turtles on Runway 4L and nearby taxiways that controllers were forced to move departing flights to another runway, airport authorities reported.

"We ceded to Mother Nature," said Ron Marsico, a spokesman for the city's Port Authority, which owns the airport.

Workers from the Port Authority and the US Department of Agriculture were scooping up turtles and moving them across the airport, he said. Flight delays averaged about 30 minutes, the FAA said.

The migration of diamondback terrapin turtles happens every year at John F Kennedy International Airport, which is built on the edge of Jamaica Bay and a federally protected park. In late June or early July the animals heave themselves out of the bay and head toward a beach to lay their eggs.

The peak of the migration usually lasts a few days, Marsico said.

Several pilots, some of them stifling chuckles, began reporting turtles on Runway 4L just as the morning rush hour was beginning at JFK, according to a radio recording.

"Be advised 30 feet (10m) into the takeoff roll, left side of the centerline, there's another turtle," called the pilot of American Airlines Flight 1009, a Boeing 767 that had just taken off bound for the Dominican Republic.

"There's another one on the runway?" asked the controller.

"Uh, well he WAS there," the pilot said as the big airliner climbed into the air.

American 663, a Boeing 737 headed to Fort Lauderdale, found its way to runway 4L blocked by three of the roving reptiles. After ground crews removed them, the plane taxied into takeoff position, received takeoff clearance - and was promptly blocked by more turtles.

American and JetBlue, which has a hub at JFK, both said there were no major disruptions to their flights.

"We hope for faster animals next time," JetBlue said in a statement.

Diamondback terrapins can grow up to 23 centimetres long and weigh up to 1.4 kilograms, but most average about half that size.

Wayward wildlife is a serious concern at JFK and nearby LaGuardia Airport, which both sit on shorelines populated by geese, turtles, ducks, frogs and other animals.

- AP