Swimmers have been warned to stay out of the water at the Egyptian resort of Sharm el-Sheikh after four tourists were attacked by a shark.

The oceanic white tip shark bit the arms off two people and seriously injured another pair in two separate incidents.

The tourists, all Russians, were taking a dip from their Red Sea beachfront hotels when the shark struck, a local conservation worker said.

Director of Sinai Conservation Mohammed Salem said the shark first attacked two people swimming in the Ras Nasrani area.

The same shark was also thought to have been involved in an attack on another Russian couple swimming close to the resort beach, he added.

The shark badly injured a woman's legs and back, and she had to be resuscitated after her rescue. It also tore the man's legs.

Diving instructor Hassan Salem said he was in the water at the same time of the attack and was circled by the same shark before it went after the couple.

"I was able to scare the shark away by blowing bubbles in its face, but then saw it swim to a woman and bite her legs," he said.

All four victims were flown to hospital in Cairo and were in critical condition.

Mohammed Salem said coast guards were hunting for the shark and have warned swimmers to stay out of the water in Sharm el-Sheikh, a favoured scuba diving destination.