MONTREAL (CBC) - A major gas leak in downtown Montreal forced about 1,000 people out of the CIBC office tower Tuesday morning.

Firefighters said the gas leak happened around 9:30 a.m., after a Gaz Metro crew hit an underground mainline while drilling through a sidewalk on René-Lévesque Boulevard near Peel Street.

People in the nearby 45-floor CIBC Tower were asked to leave the premises.

Firefighers cordoned off several blocks between De la Gauchetière, Sainte-Catherine, Peel and Drummond streets, causing traffic headaches.

The odour of gas on the scene was strong, said CBC reporter Lauren McCallum.

Two people were brought to hospital it was unclear if they suffered a malaise due to gas odours, or whether they suffered from a pre-existing condition.

Workers were allowed back into the building after the leak was capped off two hours later.

The office tower is one of the tallest in downtown Montreal.