A highrise scaffolding collapse claimed four men's lives on Christmas Eve, leaving their split staging equipment dangling more than 10 storeys above a west-end Toronto street.

Workers were on the scaffolding at an apartment building near Kipling Avenue and Steeles Avenue West on Thursday afternoon when the staging gave way.

Four of the men died when they fell to the ground just after 4:30 p.m. A fifth man is in hospital in critical condition with extensive head injuries.

They fell from the 13th floor of the 18-storey building. People who live in the building phoned 911 to report the accident, police said.

Raymond Allard, who witnessed the accident, told CBC News he heard a bang, then looked out to see the scaffolding, snapped in two, hanging off the side of the building at 2757 Kipling Ave. One worker was still attached to scaffold by his safety harness.

It is unclear if that man managed to scramble to safety.

Police say all of the men had safety harnesses, but they could not say if the harnesses were attached.

"The information we have at this time is that the five men were employed by a contracting company and they were doing repairs to balconies at this apartment building," said Const. Tony Vella.

"For unknown reasons, the scaffolding collapsed. As a result, five men fell," he said.

Four of the men were without vital signs when rescuers arrived. The fifth was taken to Sunnybrook Hospital.

The Ontario Ministry of Labour has sent investigators and Toronto police say they are assisting.

"At this time it is unclear exactly what all the details are," said Vella, "so we're still speaking with witnesses."

Police said they do not have any information to release on the victims' names or ages.