A massive search is underway for a man in his 60s after a rowboat carrying six people capsized in the River Thames.

Surrey Police said on Friday afternoon they feared the man was still in the water, hours after the small boat capsized shortly before 8.50am.

Five other people were rescued after falling into the river in Sunbury-on-Thames, and three of them were taken to hospital for further checks, authorities said.

The missing man’s family has been informed and is being kept updated, Surrey Police said.

Police, paramedics, fire and emergency services all rushed to the scene at Sunbury Lock – near the island of Wheatleys Eyot – on Friday morning following reports of people in difficulty in the water.

HM Coastguard and a local RNLI service were also called to assist in the search and rescue operation, Surrey live reported.

A woman walking her dog near the river on Friday evening said she saw a red rescue boat on the water around 10 a.m. and that there was a helicopter nearby at the same time.

The woman, who wished to remain anonymous, said: “We could see they were searching in the water, they had walkie-talkies, we could tell they were searching for something.”

North Surrey Chief Inspector Andy Jenkins said in a statement at 3pm: “This is a very distressing time for everyone involved and we continue to support our partners in the search for the missing man.

“Our investigations to establish the exact circumstances of the boat capsizing remain ongoing, but at this time we do not believe there are any suspicious circumstances or third party involvement.

“We will look to share further updates with you as we have them.”

Members of the public were asked to avoid the area while the search continued.

Located approximately 14 miles from central London, the reach above Sunbury Lock is home to several water sports clubs and is a popular destination for rowing, sailing and kayaking, with various annual regattas held in the area.