Firefighters spent hours fighting the blaze in Nipawin, a town in northeast Saskatchewan.

A house fire in Nipawin, Sask., has claimed the life of a fifth person — the mother of twin children who died a day earlier.

Melinda Whitehead, 30, who had been seriously injured in the fire that destroyed the bungalow, died overnight Thursday, the RCMP said.

The fire broke out Wednesday night. Six-year-old twins, a boy and a girl, died, as did Whitehead's husband, Larry Jobb, and her sister, Laura Whitehead, 21.

The RCMP identified the twins as Rasaun Waldbillig-Whitehead and Dashawnda Waldbillig-Whitehead.

It's the second tragedy this year to hit the town in the northeast part of the province.

Eight months ago, two men were killed when a backhoe hit a natural gas line on the town's main street and there was an explosion and fire.

A holiday tragedy

Coming just days before Christmas, this is an especially hard time of year for a tragedy like this, Nipawin Mayor Glen Day said.

"There's probably no good time for a fire like this, but this would certainly be the worst time, right before Christmas and all the kind of expectations that people have for Christmas," he said.

Investigators are trying to find out what caused the blaze, RCMP Const. Leo Martin said. Provincial fire inspectors have been called in.

The inside of the house was reduced to ashes and the roof was partially caved in following a blaze that firefighters battled for several hours. 

"There's no foul play indicated at this time. We're just covering the bases ensuring that a thorough investigation is being completed," Martin said.

Two bystanders who ran in to help with the fire were treated in the Nipawin hospital and are expected to be released soon.