A man is in hospital in serious condition after an explosion and fire forced a family of five to jump from the top floor of their Dartmouth townhouse.

Halifax Regional Fire and Emergency say they were called to the townhouse on Princess Margaret Boulevard around 2:15 a.m. Friday.

By the time firefighters arrived, the family had already escaped the home. Halifax Fire believes the father was checking the furnace in the basement when it exploded. The man found his way to the top floor, threw a small mattress out the window, and the family jumped.

“At this time we don't know what happened, what caused the explosion,” says Roy Hollett, Deputy Fire Chief of Halifax Fire. “The furnace was inspected within the last two, three days, so we're now trying to determine what exactly happen to cause that explosion and fire.”

Neighbour Brandon Marshall witnessed the family having to jump out of the window.

“They threw the kids out first,” Marshall says. “Then the mother came out and then the father came out, and his burns on his legs. He had chunks of skin hanging.”

Marshall says he took the family into his home to stay warm.

“The lady was completely, had nothing on, all their clothes burnt off,” he says. “All she had was a blanket and an old pair of pajama shorts.”

The family was sent to hospital. The extent of all their injuries is unknown at this time.

Neighbours tell CTV News the family were newcomers and were not living in the townhouse that long.

“The back is destroyed. You can see the levels come out like this and then back in and everything is burnt to a crisp on either side. There's damage to both apartments on either side of them,” says neighbour Julie Corwell.

Fire officials say there is significant damage to the unit in which the fire originated, and minor damage to the two adjoining units, displacing two other families.

The Canadian Red Cross is assisting with clothing and food for the affected families.

At the peak of the fire, there were eight vehicles and 40 firefighters on scene. Chief Hollett is calling the case a puzzle, as it’s rare for a furnace to explode.

"The door was blown off the frame and the windows were also blown out. Between the doors and the windows there were about 50 to 60 feet blown from the house, so they knew an explosion had occurred," he says.

A GoFundMe page has raised $3,900 for the family in just 12 hours.

With files from CTV Atlantic’s Laura Brown.