A light plane has made an emergency landing on a packed beach in Portugal, killing a 56-year-old man and an eight-year-old girl who were sunbathing, authorities say.

Hundreds of sunbathers were on the popular beach at Caparica, 30 kilometres south of Lisbon, and witnesses said some people ran into the sea to avoid the plane.

The National Maritime Authority said the man and girl died on the beach.

Officials said no other people were injured.

The small plane landed during the busy late afternoon. ( AP: Armando Franca )

The two occupants of the plane were unhurt and were being questioned by police.

The small aircraft, reportedly a Cessna, appeared to be in difficulty and wobbled as it skimmed low over the sunbathers, scattering them and spreading panic on the beach, witnesses said.

The plane appeared to have a partly broken left wing, which hung lower than the right wing, Portuguese television pictures showed.

Officials said the accident happened late in the afternoon.

Sao Joao de Caparica beach is one of the closest to Lisbon and draws big crowds in August, when the Portuguese take their main summer holidays.

The dead girl was with her parents, who were unhurt, witnesses told local television channels.

AP/Reuters