Classes were cancelled and about 500 children were sent home from a Port Moody, B.C., elementary school after two students fainted and were taken to hospital, says a school district spokeswoman.

Not long after the Aspenwood elementary students fainted during a singing rehearsal Thursday morning, the principal of the kindergarten-to-Grade-5 school called in emergency officials, said Cheryl Quinton.

"Paramedics were called just because there were two children involved," she said. "The principal called the paramedics and they recommended that as a precaution -- they didn't see anything overtly evident -- but just as a precaution take them to hospital and get them checked out."

Firefighters also arrived on scene, she added, and asked for the school to be evacuated while they conducted an air-quality test, which found nothing amiss.

Firefighters then decided to perform more tests, said Quinton.

"So the kids got released early and the parents picked them up," she said.

Quinton said the school district will update its website to let parents know if the school will be open Friday.

It was unclear what may have caused the children to faint, she said.

The Coquitlam School District has 45 elementary, 13 middle and nine secondary schools, serving about 30,000 students in Belcarra, Ioco, Anmore, Port Moody, Coquitlam and Port Coquitlam.