A British tourist has fallen 80 metres to his death off a waterfall in the Blue Mountains, west of Sydney, police say.

Officers were told the man, believed to be aged in his 20s, fell at Wentworth Falls at around 2.15pm on Sunday.

Police were last night at the scene, but high winds stopped them from finding the man's body.

A witness told the ABC she had seen a group of friends gathered on some rocks.

''Then they went down to the next one and I knew something was going to happen,'' she said.

''We just saw them all panic and a 20-year-old boy fell over 100m down the waterfall.''

The NSW Police spokeswoman said officers from Police Rescue will walk into the bush today to try and reach the man's body, before Polair is called in to winch it out.

The spokeswoman said the man was a British tourist and was at the waterfall with friends.

"We don't know how he's come to fall off," the spokeswoman said.

At Coogee beach yesterday, a 31-year-old man sustained critical head injuries after falling from a wall he was climbing.

AAP and smh.com.au