Ottawa police and the Ontario Fire Marshal's office are investigating three suspicious fires that destroyed several local businesses, left 30 people without jobs, and caused millions of dollars in damage overnight.

The biggest of the three fires blew out windows at a strip mall on Richmond Road, which is best known for Rockin' Johnny's Diner.

Emergency crews say the building was fully engulfed in flames when they arrived at 2:50 a.m. Friday. It caused about $5 million in damages and completely destroyed five businesses.

It took 77 firefighters to get the flames under control at the strip mall at 1463 Richmond Rd.

The owners of the restaurant told CTV Ottawa they're not sure if they're going to rebuild. In the meantime, 18 employees at the restaurant are out of work.

"It's really sad, and I don't know how to handle this. It's a heartbreak," said co-owner Rathinadillai Jegatheesvaran.

Earlier Friday morning, a downtown business called Oil Changers Automobile also went up in flames.

Firefighters say the blaze began inside the building at about 1 a.m. and heavy smoke prevented them from entering.

A neighbouring Tim Horton's restaurant was damaged by flames, and a nearby house was evacuated as a precaution. Damage is estimated at $700,000.

Meanwhile, a series of small explosions woke up residents in Old Ottawa South after a commercial building in that neighbourhood went up in flames at about 11:45 p.m. Thursday.

Fire officials say the second floor of the two-storey building, which houses West Coast Video and Elee Spa, was fully engulfed in flames when crews arrived.

At midnight, the blaze was categorized as a three-alarm fire.

District Chief Det. Lyle Fraser said the intensity of the three fires strained Ottawa's fire services, which struggled to find the resources needed to battle all of the blazes.

He says although all fires are considered suspicious, there's no reason to believe they are related.

"We have no indication of links to one another at the moment," he said.

No injuries were reported in any of the fires.

Anyone with information is asked to call Ottawa police at 613-236-1222 ext. 5190 or Crime Stoppers 613-233-TIPS.

With a report from CTV Ottawa's Vanessa Lee