Transformer blasts rock downtown Toronto

Explosions from a transformer fire has rocked Toronto's financial district for hours, prompting police to close off a section of the downtown area as heavy smoke billowed up from subway grates.

The blast on Monday afternoon shut down several blocks during rush hour but Toronto police say no injuries have been reported.

A fire in a transformer in an underground electrical vault caused thundering explosions that continued intermittently for hours, Toronto Fire Captain Adrian Ratushniak said.

The cause of the fire, which prompted the evacuation of a bank tower, was not yet known and would be investigated, he said.

Previous, similar fires have been caused by water, deteriorating electrical connections or aging transformers, he said.

Firefighters had the blaze under control, Ratushniak said.

"Hydro vaults (electrical transformers) are relatively contained" because of the concrete boxes encasing them, he said.

"You don't typically see flames visible."