An Adelaide man has been arrested after police discovered commercial explosives in an apartment in the city centre.

The discovery was made about 9.30am on Wednesday when officers searched a property on Grenfell Street following a public tip-off.

Inspector Michael Walsh said the footpath and a walkway was cordoned off for several hours while the bomb squad examined the explosives at the scene.

“The bomb squad have confirmed it is an explosive device, it is commercial explosives,” he told reporters.

He said police also located a 22-calibre firearm, an air rifle, drugs and drug paraphernalia.

A 40-year-old man at the apartment was arrested and is expected to be charged with firearms, explosives and drugs offences.

Inspector Walsh said police do not believe there is any further risk to the public or that the discovery is terror-related.

“We haven’t exactly confirmed what the explosives were but all explosives do have the potential to cause danger so that’s why we have had this response,” he said.

He said it was “very unusual” that such an incident would happen in the CBD.

“Because it’s such a populated area, we’ve had to put all resources in to ensure everyone’s safe,” he said.