Sydney - Police on Thursday said an Irishman missing after last being seen in a Sydney pub has been found at the bottom of a stairwell after apparently being trapped for five days.

Donal “Donie” O'Sullivan was last spotted at the bar in Bondi on Saturday morning but never made it home.

He was reported missing on Sunday night by relatives, sparking a search by friends and the local Irish community with more than 800 people joining a Facebook page dedicated to finding him.

The 33-year-old was eventually found on Wednesday lying in an emergency stairwell of a commercial building just metres away from where he was last seen, suffering head and back injuries.

Police said they were treating the case as possible “misadventure”.

“Emergency services were called and he was taken to St Vincent's hospital in a serious condition, suffering head and back injuries,” police said.

“Police are continuing to investigate how the man sustained his injuries. Following initial inquiries, misadventure may have been the cause of the man's injuries.” - AFP