There were 100 railcars in the train. CN said 26 left the tracks in the derailment. (Liam Richards/The Canadian Press)

A major train derailment has occurred near Wadena, Sask., prompting authorities to keep people well back from smouldering railcars and smoke that may be toxic..​

The CN Rail derailment happened at 10:40 a.m. CST Tuesday about 20 kilometres west of the town of 1,300, which is about 230 kilometres east of Saskatoon.

There were no reported injuries. CN said two employees were on the train at the time of the derailment and both are safe.

Motorists in the Watson area were forced to take alternate routes to stay clear of the derailment. (Peter Mills/CBC) Officials are worried about toxic smoke from the burning cars and are keeping people eight kilometres from the scene.

"It's huge," Alison Squires, editor of the Wadena News, told CBC News describing what she saw shortly after the derailment. "It's like taller than a [grain] elevator."

About 50 people were evacuated from Clair, a small community about one kilometre from the crash. People were also evacuated from other farm homes in the area, the RCMP said.

Students at the school in Wadena were being kept indoors during the school day.

"Huge plumes of smoke and fire," Squires said. "RCMP and obviously local fire departments are there. They're detouring traffic."

Jason Evans, who lives in Clair, Sask., is worried about livestock he has in the area and smoke from the fire. (Peter Mills/CBC) A spokesman for CN said the train was hauling 100 cars, 26 of which derailed.

Six of them contained hazardous materials, including four that had either hydrochloric acid or caustic soda.

The other two had petroleum distillates, CN said.

Heavy smoke and fire were seen coming out of the crashed cars for several hours. By late afternoon, the smoke had diminished. Access to the site was limited, but observations from just outside Clair suggested the fire had been put out.

Traffic is being detoured around routes that may be downwind of the derailment, and provincial government officials said detours will remain in place until the areas are safe.

"I'm concerned for my animals," Jason Evans, who lives in Clair, said Tuesday. He said he has livestock in the area near the crash site.

"I've got 600 head of buffalo there," he said, noting that smoke appeared to be heading in their directions. "It's going over the top of my pastures, its going over the top of my hay field.

"Is that going to affect my hay and my livestock is what I'm kind of interested to find out," he said.

In a statement issued Tuesday afternoon, the province said a rapid response team made up of emergency management and fire safety experts had been sent to the scene along with specialized air quality monitoring equipment from the Environment Ministry.

"Environment [officials] will be monitoring air quality in the area," the statement said. "They will be working with CN and the local officials as part of a co-ordinated response."

Evacuation centre in Wadena

People who were told to leave the area, from Clair and rural homes, are being sent to Wadena where an operations and reception centre has been set up.

There was no immediate word on how long the evacuation order will be in effect, but officials said a media briefing and update would be provided Wednesday at 11 a.m.

A CN hazardous materials team was seen en route to the site.

Officials from the Transportation Safety Board of Canada were on their way to the site.