A Libyan army medical plane crashed south of Tunis early on Friday, killing all 11 people on board, Tunisian emergency services said.

"The plane crashed at 1:30 am (0030 GMT)... with 11 people on board — three doctors, two patients and six crew members," spokesman Mongi El Kadhi said.

He said there were no survivors from the accident in the Grombalia area, 40 kilometres (25 miles) from the capital.

"The whole plane was completely burnt out. The emergency services went to the crash site and recovered the charred bodies."

Shortly before the plane disappeared from radar screens, the pilot radioed the control tower at Tunis airport to say an engine had failed, emergency services told an AFP journalist at the crash site.

The aircraft crashed in a field on the edge of the village of Nianou but managed to avoid any houses, the journalist reported.

The Libyan flag was still visible on the tailplane amid the wreckage.

At daybreak, teams began searching for the aircraft's black box flight recorders in a bid to establish the cause of the crash.

There was no immediate word on the identities of the two patients on board or why they were being flown to Tunis.

The aircraft was a Soviet-designed twin-propeller Antonov-26, Tunisia's Mosaique FM radio reported.