Twenty children in western Japan were taken to hospital amid complaints of a sulfur-like smell at their school. Fire department officials say they are slightly ill.

The elementary school in Toyonaka City, Osaka Prefecture, notified the fire department of the odor shortly after 9 a.m. Tuesday.

Footage taken by NHK shows more than 10 ambulances and fire trucks parked on the school grounds and fire fighters going in and out of the building.

Fire department officials say the children are between the ages of 7 and 11. They say they did not find any abnormalities when they used gas detectors to inspect the school and are looking into the cause.

The unaffected children were taken to the gym by around 11 a.m. and parents could be seen coming to pick them up.

A sixth-grade boy said they were taking a test when everyone started to complain about an odor, after which an announcement instructed them to evacuate to the gym.

He said when he asked what had happened, he was told that the cause was unknown.