Adelaide police now say they don't believe a fire that affected up to a dozen Chinatown businesses was deliberately lit, after earlier describing it as "suspicious".

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The Metropolitan Fire Service said firefighters arrived in Grote Street shortly after 1:00 am to find "an intense fire" in a shop that was burning through the roof and rapidly spreading to neighbouring shops.

More than 70 firefighters then worked to put the fire out and they contained it within an hour.

The MFS said the fire's "rapid spread" meant that three shops were "significantly impacted", with two — a supermarket and a restaurant — being gutted and a third that sold shoes and clothing being heavily fire-damaged.

"There was a pretty bright orange glow coming from the top [of the building complex]," the MFS's David Juniper said.

"Very heavily smoke-logged internally. So it was very hard to determine where the origin of the fire was and where our initial attack point should be with crews."

A firefighter checks out one of the damaged shops. ( ABC Radio Adelaide: Spence Denny )

The fire caused smoke to drift across most of metropolitan Adelaide. It was fully extinguished shorty after 6:00am, but firefighters remained at the scene throughout the morning to clean up.

Zhong Lim has run a grocery store on Grote Street for 14 years said that he was alerted to the fire by a monitored smoke detector.

"I feel depressed…we have six staff…we have insurance," he said.

Some of the damage seen from Grote Street mid-morning. ( ABC News: Sarah Hancock )

Shop owner C.K. Lim went to the scene just after the fire was reported and said he had not yet been able to access his business.

"We just saw smoke and we saw a lot of fire brigade around at one-thirty," Mr Lim said.

The MFS said that damage is estimated at $1.5 million within a complex valued at up to $4 million.