OTTAWA -- Two firefighters were taken to hospital after rushing to contain a fire at a three-storey building in Lowertown Thursday afternoon.

The fire broke out around 2:30 p.m. at 46 Nelson Street, an unoccupied building near Murray Street under renovation.

Officials said a second alarm was declared because of the weather conditions. A heat warning remains in effect for the capital.

The two firefighters were taken to hospital as a precaution because of the heat.

“You can’t have enough people on scene to be able to rehab the guys, when they come out after going through one tank, working for half an hour, they need at least double that time to rehab," Platoon Chief Rodney Fleck said at the scene. "Unfortunately we need crews there all the time, if we take crews out and don’t put them back in right away, this is going to get away from us.”

Firefighters remained on scene throughout the afternoon. Most crews started to clear the scene around 6 p.m., but some will continue to monitor hot spots for a few more hours.

It was at least the third fire that crews battled in Thursday’s scorching heat.

Thursday morning, fire crews contained a fire to one side of a three-storey residential building on McGillivray Street in Old Ottawa East.

And early Thursday morning, fire crews brought a blaze under control in a detached garage on Spruce Street in Little Italy.

No injuries were reported in either of those fires.