"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.

A Spanish national died, it added. An air force spokeswoman told AFP the victim was the pilot of one of the aircraft involved in the collision.

Another pilot with Portuguese nationality was lightly injured and received emergency treatment before being rushed to Beja hospital, the air force said.

Portugal's Defence Minister Nuno Melo called it a "tragic accident" and told reporters an investigation would be opened "to determine the exact cause" of the collision.

President Marcelo Rebelo de Sousa said: "It was meant to be a moment of leisure and shared enjoyment. It turned into a moment of pain."

The air force said the six aircraft belonged to an aerobatic group made of up Spanish and Portuguese pilots named the "Yak Stars".

The planes that collided were Yakovlev Yak-52, a Soviet-designed aerobatic training model.

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 in a cloud of smoke.

One plane crashed outside the airbase's grounds and the second involved in the accident managed to land on the airport tarmac, with no victims among the spectators, the air force said.

According to the Beja Air Show's website, the "Yak Stars" were participating with around 30 other European aerobatic groups. Organisers billed them as southern Europe's largest civil aerobatics group.

The air force said organisers of the show at Beja airport had suspended the event, which began on Saturday.

The force expressed its "most sincere condolences" to the relatives of the pilot who died.