American singer Jimmy Buffett was taken to hospital overnight after falling face first off the stage during a concert at Sydney's Hordern Pavilion.

The 64-year-old musician was performing a final encore when he fell off the stage onto the concrete floor.

The performance was stopped and patrons were asked to leave the premises while Buffett was treated.

Renowned St Vincent's Hospital emergency doctor Gordian Fulde was in the audience, just metres away from the musician when he fell.

Dr Fulde treated him on the scene and later at the hospital.

"I thought he'd broken his neck," he told 702 ABC Sydney.

"I heard the clunk of his head on a metal ledge, he has a deep gash on his scalp, which is all right now.

"But at first I thought - this guy is going to be a spinal injury."

A St Vincent's Hospital spokeswoman says Buffett is in a stable condition.

One concert-goer, Sue, says the singer did not have time to put his hands out and hit the floor face first.

"He just went over to the edge of the stage, like he had numerous times through the night, just to wave, and people were throwing stuffed toys and things at him," she said.

"And he just took one step too many and just disappeared in a flash.

"He didn't have time to put his arms out to save himself or anything, he just dropped."

Buffett has released more than 30 albums and has been touring since the late 1970s.

He is known for a country folk and island musical style which includes hit songs Margaritaville and Cheeseburger In Paradise.

According to Buffett's website, the next stop on his tour is scheduled for January 29 in Auckland, New Zealand.