West Australian police say it is fortunate no-one was killed or seriously injured when part of a wall collapsed outside a busy Perth nightclub early this morning.

The Library, in Perth's entertainment district Northbridge, had been hosting an event called Thirsty, advertised as an end-of-exams party for students featuring "strippers, cheeseburgers, whipped cream and champagne".

It was filled with people when part of a side exterior wall fell from the two-storey structure about 3:30am.

Bricks came crashing down into a fenced carpark and on a footpath near pedestrians outside the Lake Street venue.

How the left-hand side wall looked before the collapse. ( Google Maps )

Police officers already happened to be outside, having earlier been called to deal with a man allegedly abusing a bouncer.

"There (were) some of our officers from Perth present when the wall collapsed, and they've actually captured some of it in footage on their body-worn cameras," Senior Sergeant Jamie Brennan told the ABC.

"They heard a loud crashing noise and saw a lot of dust and people obviously quite alarmed by the incident."

Bricks fell on the footpath outside the nightclub. ( ABC News: James Carmody )

The officers immediately evacuated the venue and closed the street.

Senior Sergeant Brennan said officers checked to make sure there was no-one beneath the rubble before firefighters arrived and confirmed it by using thermal imaging devices.

Senior Sergeant Jamie Brennan said it was very lucky no-one was injured. ( ABC News: James Carmody )

"I think we're very, very lucky that no-one was seriously injured or killed. It's a good day for us," he said.

"It was a good result, it could have been much worse, so very fortunate."

He said the collapse had happened at what was likely one of the busiest places in the state at that time of the morning.

The nightclub will remain closed until it is deemed safe by City of Perth structural engineers.

A spokeswoman for WA Police declined to release bodycam footage showing the wall's collapse, saying it was not a police matter.