The Ottawa construction company responsible for the gas leak that forced the evacuation of several downtown buildings and the closure of roads Tuesday has apologized for the mishap.

Ottawa Greenbelt Construction, a subcontractor for light rail constructors Rideau Transit Group, was working at Queen and O'Connor streets when a gas line was severed just before 1:30 p.m.

An excavator clipped the line, causing a loud hissing sound, forcing the closure of roads for several blocks around the site of the rupture and sending thousands of office workers home early.

It was an unfortunate situation and we apologize for that. - Dale Harley, Ottawa Greenbelt Construction

Bus service ground to a halt in the downtown core, leading to major traffic delays and huge crowds at bus stops.

Dale Harley, spokesperson for Ottawa Greenbelt Construction, said the company had a map of utilities showing the gas line 30 centimetres from where the crew was working when the rupture occurred.

"It was an unfortunate situation and we apologize for that, as do our partners," said Harley. "The good news is that the emergency was well-managed by the city."

Surface work tied to LRT project

The above-ground work is tied to the $2.1-billion Confederation Line project, overseen by RTG.

RTG's technical director Peter Lauch said the gas rupture will have no impact on the June 1 deadline to have the majority of the surface work, including streetscaping, completed in time for the summer tourist season.

However city officials have already warned the work on Rideau Street, where a sinkhole appeared last June, won't be finished in time to meet that deadline. Nor will parts of Queen Street, the city has said.

Lauch called the gas leak an "isolated incident" that caused only a "minor" delay in RTG's work schedule.

"As far as RTG is concerned, we're committed to meeting our obligations," Lauch said.

The Technical Standards and Safety Authority is investigating the gas leak, according to a spokesperson from the provincial body.