One of the world's largest passenger jets had to make an unscheduled landing at Darwin airport overnight.

The Qantas A-380 aircraft, en route from Sydney to Singapore, put down in Darwin because of a medical emergency on board.

A Darwin International Airport spokesman says it is the first time an A-380 has landed at the airport.

It came after a 59-year-old male passenger suffered a seizure during the flight.

The aircraft was met by emergency service personnel and the man was taken by ambulance to Royal Darwin Hospital.

The A-380 took off for Singapore a short time later.