The authorities have found the body of a 41-year-old man who went missing on Sunday afternoon while snorkelling alone near Sisters' Islands Marine Park.

The police said in an update yesterday they found and retrieved the body at around 5.45pm.

They had mounted a search and rescue operation on Sunday for the man, together with the Maritime and Port Authority of Singapore and the Singapore Civil Defence Force. The police received a call for assistance at about 12.40pm on Sunday.

A park visitor who was on the island that day told The Straits Times that the man's wife had approached him at about noon to ask if he had seen her husband.

The visitor, who wanted to be known only as Mr Ariff, said the woman, who looked panicked and appeared to be in her 30s, described her husband as big-sized and said he had been missing for four hours. The 25-year-old goods vehicle driver said the woman told him her husband had planned to snorkel for 30 minutes.

"We were shocked, because he'd been missing for so long and we had just arrived in the area," Mr Ariff told ST.

With his friends, he went into the water where the man was last seen snorkelling, but said it was very deep and the currents were too strong. While they were swimming, they noticed police boats circling the area and officers walking around the island, presumably in search of the missing man, said Mr Ariff. He left the island at about 4pm with his friends, and added that it was raining heavily as he left.

The police are investigating the unnatural death.