Firefighters spent more than seven hours extinguishing flames after an explosion and fire inside a grain elevator in the south end of Halifax.

City and fire officials evacuated several blocks around the burning building, forcing as many as 400 people to leave their homes for most of the day.

The ground shook from the force of the explosion.

"We were really concerned for our kids, so we just grabbed them and started running in the other direction," said Judy Walsh who lives near the elevators.

John Blandin of the Halifax Fire Department said the city hasn't felt anything like it in years.

"It was a good sized explosion. It dislodged a few walls," he said.

It's not known what caused the blast, but Blandin says grain elevators can fill with dust that can easily ignite.

"Elevators are notorious for causing explosions, but we're not sure if that's what caused this one," he said.

For almost 75 years the elevators have stored a variety of materials.

Michelle Peveril of the Halifax Port Authority, the agency that owns the building, says there were no injuries.

"We have been extremely lucky that all of the staff are accounted for and no injuries have been reported," said Peveril.

More than 400 people were ordered out of their homes, but were allowed to return late Thursday night.