An American surfer has been killed in a shark attack off Mexico's southern Pacific coast, officials said today.

The San Francisco man bled to death yesterday after a grey shark bit his right thigh, leaving a 38-centimetre wound, the Guerrero state Public Safety Department said in a statement.

The US Embassy in Mexico could not immediately confirm the man's name, but local authorities identified him as a 24-year-old who was surfing with a fellow American. The other man was not injured.

The attack occurred at the Troncones beach, about 45 minutes west by car from the beach resort of Ixtapa.

The statement said the victim suffered wounds "that reached from the hip to the knee, exposing the femur".

The victim was still alive when he was brought back to the beach. It took so long for the ambulance to reach the relatively isolated and undeveloped beach that a bystander took the victim to a local hospital in his car.

The man died a few minutes after reaching the hospital from loss of blood, according to the statement.

Shark attacks are relatively rare in Mexico.

In 2006, the International Shark Attack File at the Florida Museum of Natural History reported only one attack in Mexico, which was not fatal.

AP