A man is in a serious condition after he was attacked by a shark at a South Australian beach.

Emergency services were called to Port Noarlunga Jetty, south of Adelaide, at about 9.45am local time (10.15am AEST) after reports a swimmer had been bitten.

Ambulance services said the man was aged in his 40s and suffered an injury to his thigh.

He was taken to Flinders Medical Centre in a serious condition.

Swimmers have been evacuated from the water and police urge people to avoid the area.

More to come.

Source Credit: 9 News