Police have arrested a man who climbed onto the roof of a building in Adelaide's CBD and was allegedly wielding a knife.

Key points: Police said the man was spotted carrying a knife on South Terrace

Police said the man was spotted carrying a knife on South Terrace He was located nearby but allegedly ran away and hid inside a roof

He was located nearby but allegedly ran away and hid inside a roof Nearby businesses were evacuated as the situation unfolded

Witnesses said they believed the man gained access to the roof of the Gilbert Street IGA supermarket via a side stairwell.

The road was closed and nearby businesses were evacuated as the situation unfolded.

A worker at the supermarket said the man had earlier entered the store asking to use the toilet.

He later saw the police sprinting after him and the supermarket was then evacuated for about an hour.

"It's all going down at the Gilbert Street IGA," the male employee said.

Chief Inspector Matt Nairn said a woman called police about 8:00am reporting a man carrying a knife on South Terrace.

Police officers in front of the IGA in Gilbert Street in Adelaide's CBD this morning. ( ABC News: Richard Davies )

The 26-year-old Oaklands Park man was tracked down but he allegedly ran away and hid inside the roof of the supermarket.

Police then used a drone and dogs to surround the area.

Chief Inspector Nairn said the man was arrested by STAR Group officers when he broke through the roof, where they were waiting.

Police used a drone as they searched for the man. ( ABC News: Richard Davies )

He said police believed the man was "wanted for other matters", including theft.

"Any time anyone runs from police [and] we think they might be armed, we certainly need to consider public safety and we follow it through," he said.

"The simple fact he's gone into a building and done the extra step to hide in a roof space indicates his behaviour is somewhat erratic."

He said he did not know whether the man had a weapon on him when he was arrested.

The man has been charged with property damage, unlawfully being on premises, unlawful possession and hindering police.

He was refused bail and is expected to appear in the Adelaide Magistrates Court today.

Witness Wayne Henry said he was in an online meeting with colleagues from overseas when he heard two men run through the hallway outside his office, which is above the supermarket.

The man who was later arrested then got into the roof and hid.

"I'm yelling and screaming and the guys on the Zoom conference are like 'this is the weirdest Zoom conference I've ever been on, all this drama happening in the morning'," Mr Henry said.