The body of a man who went missing at a Sydney swimming hole has been found.

Emergency services were called to Bents Basin about 11.30am this morning after a group of men, believed to be aged in their 20s, were struggling in the water, police said.

Bystanders rescued three men, but a 25-year-old Nepalese national did not resurface after disappearing underwater.

His body was found in the water about 1.30pm after a search by police divers, Fire and Rescue NSW, ambulance and the State Emergency Service.

Police divers have located the body of a man, believed to be a 25-year-old Nepalese National at #BentsBasin after he went missing while swimming https://t.co/EQOr31rYx3 — NSW Police Force (@nswpolice) 27 January 2019

One 32-year-old male witness who spoke to The Daily Telegraph said he was swimming at the basin when he heard screams coming from the other side.

“We were swimming and suddenly we heard all this screaming,” he said.

“We swam over and they said someone’s drowned. Rangers then got on the PA and said ‘everyone out.’”

According to the witness, there were hundreds of people in the water at the time, as the Sydney-siders attempted to cool off as temperatures in the area reached nearly 38C.

The man is yet to be formally identified and a report will be prepared for the coroner.

Meanwhile, the search is on for a second man who disappeared while swimming in a river in NSW’s Shoalhaven region this afternoon.

At about 3.40pm, a 27-year-old man was swimming with friends in the Kangaroo River near a camp ground at Bendeela, when he was seen to disappear underwater and not resurface, police said.

Rescue workers were told the man was on an inflatable mattress before he disappeared.

Assistance has also been sought from police divers who are currently travelling to the scene.

Also, a report was prepared for the coroner following the death of a man in the Murray River, on the Victorian border, yesterday afternoon.

About 12.30pm on Saturday, a 37-year-old man entered the Murray River at Yarrawonga, Victoria, when he began to struggle to stay afloat.

Members of the public called for help and tried to assist the man, who eventually went under the water.

Officers from both NSW Police and Victoria Police attended, and about 1.10pm the man’s body was recovered.

NSW Police were investigating the circumstances surrounding the incident.