"The air force regrets to announce that at 4:05 pm (1505 GMT), at the Beja Air Show, two planes were the victim of an accident during an aerial demonstration" involving six aircraft, it said in a short statement.

Portuguese media reported that the pilot of one of the aircraft had died.

They identified the aircraft as two Yakovlev Yak-52, a Soviet-designed aerobatic training model.

The air force said emergency services were at the scene and organisers of the show at Beja airport had suspended the event.

A video filmed by a spectator and posted on social media showed a formation of six planes in flight, with one of them ascending, apparently touching one of the others and then crashing to the ground.

Portuguese newspapers quoted witnesses as saying the six aircraft were part of an aerobatic group named the "Yak Stars".

They said organisers of the event presented it as the biggest civil aerobatics group in southern Europe.