Fire officials have ruled out a gas leak at Woodlands Elementary School in Calgary's southwest, after 14 students were taken to hospital and the school was fully evacuated.

It was initially believed a carbon monoxide alarm was activated just after 9 a.m. MT but officials have since confirmed that was a false report.

"[It's] a bit of a mystery as to what's caused this series of symptoms with these students," said fire department spokesperson Carol Henke.

The students who reported feeling nauseous had "mild symptoms" and were taken to hospital as a precaution, according to Henke.

The Calgary Fire Department, its hazardous materials team and EMS were on scene throughout the morning. Fire officials eventually said they had not detected any dangerous materials in the school.

Classes are set to resume today but a spokesperson with the Calgary Board of Education says students are welcome to go home with their parents.

Evacuation procedure

The band room was initially evacuated, then the whole school of 290 students.

Students were loaded onto city transit buses to keep warm.

Many parents gathered outside the school. They were told told students would be shuttled via the buses to a nearby hall.

Mohammed Baber's 11-year-old daughter was one of the children treated.

"My daughter was not feeling well, having some vomiting; she fell down and was weeping when I came here," said Baber. "I was the first person who came here before these ambulance crews."

ATCO Gas was also notified.