Health authorities are still looking for clues to the suspected bug that left 10 children in hospital, 22 others sick and forced the evacuation of their school in Brisbane’s south on Wednesday.

An emergency services spokeswoman said the incident began when a nine-year-old girl suffered a medical condition, possibly a seizure, at Wellers Hill State School, Tarragindi just after 9am (AEST).

“She may have fainted, or nearly fainted, she definitely had some kind of medical incident,” the spokeswoman said.

The school was evacuated shortly after when nine other children from year four complained of nausea and upset stomachs.

Several fire and ambulance crews were called to the school where 22 children were assessed on site while nine other children were taken to hospital.

Three police crews initially attended the scene after receiving emergency calls to triple-0.

Parent Julie Owen told reporters her son had suffered a headache and tummy pains but was now fine.

Queensland Ambulance paramedic Matthew Hannabery told reporters around 10 to 15 children reported headaches, dizziness and nausea within 20 minutes of the first girl’s possible seizure.

Queensland Fire and Rescue Service officer Damien Reid told reporters they had no idea what caused the emergency.

“We’ve been able to rule out the usual suspects, for this kind of thing, the key irritant type chemicals,” Reid said.

“We’re just coming out of winter, there’s plenty of bugs going around, I couldn’t say.”

Other children, teachers and school staff were evacuated to locations within the school grounds before being allowed to return just after noon (AEST).

An emergency services spokesman said Queensland Fire and Rescue Service scientific officers conducted thorough tests at the school which came back clear.

Two samples that were sent to be tested came back clear this afternoon and the remaining test results will be received tomorrow morning.

Education Queensland has informed parents of the children of the incident and will send a letter home with students.