Sexsmith, Alta., residents have been told it's safe to return to their homes Thursday morning following a train derailment.

About 150 households in the town north of Grande Prairie were under a voluntary evacuation order Wednesday night after three train cars carrying fertilizer derailed Wednesday evening.

The voluntary evacuation orders were made as a precautionary measure due to the risk of a leak from the anhydrous ammonia stored in the derailed cars, said Sexsmith Mayor Claude Lagace.

"There will be plenty of sirens and warning if they need to evacuate. Until then, they’re not required to evacuate and the risk, apparently, is quite low according to CN people.”

Lagace said residents in about 150 houses, all within about 500 metres of the tracks, have been given the voluntary notice.

“At the moment there is no risk, we’re just making people aware if a leak does happen and it is more serious.”

However, he added there is “no chance of explosions or anything.”

Roxann Flewwelling, one of the residents living in the voluntary evacuation zone, described it as about one third of the town.

“About 20 minutes ago we had a knock on our door from a police officer telling us that we were under a voluntary evacuation notice," she said Wednesday. "We could stay in our homes if we wished, but it could quickly turn into a full evacuation so we should really get things ready.”

Many of her neighbours have already left, she said.

“Half our street’s gone already.

“After Lac-Mégantic this summer I think we all became more aware of what it was to live in a rail town where you have oil and chemicals and … other gaseous substances nearby. I could almost hit the railroad tracks from my house if I had a good arm on me.”

Flewwelling said she has packed up all the necessary belongings to leave her house, should it come to that.

Meanwhile, a command centre has been set up for Sexsmith residents in need of shelter as CN crews work to re-align the cars.

Lagace said the cause of the derailment is not yet known, but did say the tracks have been undergoing repair work over the past few weeks.