Several buildings near Parliament Hill were evacuated Tuesday after a large gas leak halted construction in downtown Ottawa.

Officials say construction crews struck a pipe shortly after 1 p.m., causing a loud explosion and a strong smell of gas in the air. High-pressure gas could be heard escaping from the broken line for several hours.

At least four buildings were evacuated and four city blocks shut down for safety measures, Ottawa police said.

A witness says she saw construction workers flee the area and shout, 鈥淚t鈥檚 gonna blow!鈥�

鈥淎ll of a sudden, you saw all the construction workers just scatter. They ran and ran and ran,鈥� said Emily Fleck, who works at a nearby Starbucks.

The Parliament buildings were not evacuated, and question period in the House of Commons continued on schedule Tuesday.

There were no reported injuries, according to Ottawa鈥檚 deputy fire chief.

鈥淚t鈥檚 only dangerous really when we get into the flammable ranges of the gas, and the gas reaches an ignition source. So that鈥檚 why we evacuated people (from the buildings),鈥� Deputy Chief Kim Ayotte said Tuesday.

Long traffic queues clogged nearby streets as vehicles were forced to avoid the route during rush hour. Public transit was also delayed, with buses forced to detour around the cordoned-off blocks.

The scene at Queen Street and O鈥機onnor Street has since been 鈥渟tabilized,鈥� Ayotte said. The roads were reopened around 6 p.m.

鈥淚 can assure you that the air quality 鈥� never was in a range that was dangerous to anybody that was in any of those zones,鈥� Ayotte said.

Many people have since returned to buildings within the evacuation zone.

With files from CTV Ottawa