Police have had to cut a man out of a wall to arrest him after he was seen entering a bathroom and never came out.

A man was found asleep in a wall cavity after crawling through a manhole in an apartment building's bathroom. Credit:Vince Caligiuri

Staff at an apartment building on Elizabeth Street in Melbourne's CBD watched the strange scene unfold from about 3am on Thursday when the 31-year-old homeless man entered a bathroom in the foyer.

Three hours later he had still not emerged. At 6am staff investigated and realised he had crawled through a manhole in the bathroom into the roof.

Police were called and found the man asleep in a wall cavity.

They said he had been crawling through the roof when he fell into the wall.

The man was cut from his confined napping spot and arrested on outstanding warrants for burglary and theft offences.