About 750 people won't be allowed to return home Monday night after an electrical blast at an apartment building east of downtown Ottawa sent one person to hospital and left the building without power.

Firefighters were called to a working fire that involved an explosion at an electrical panel at 1244 Donald St. at about 1:45 p.m. Monday.

The blaze caused smoke to spread to the first three floors of the 16-floor building. However, the fire was contained to the electrical panel on the main floor and an electrical vault in the basement.

"We were sleeping when we heard the alarm. The first thing we did was run down the stairs and we came to the main front, so we're sitting outside and all of a sudden we hear an explosion, one big explosion and after it was more explosions," said Anas Arab, who lives in the building.

One man was taken to hospital to be treated for burns. He is in serious but stable condition. Another person was treated for smoke inhalation.

Hydro was cut off to the building Monday afternoon, and residents won't be allowed to return home until the Electrical Safety Authority has deemed the building safe.

OC Transpo buses were at the scene Monday to transport people to emergency shelters, such as the Overbrook Community Centre. The city's emergency planning team, bylaw officials and social service workers were also called in to help.

With a report from CTV Ottawa's Karen Soloman