Emergency services assist school children out of the Civic Theatre onto Esk Street on Tuesday afternoon in Invercargill

Nine children have been taken to Southland Hospital after they fainted on stage while rehearsing for a singing show.

St John spokesman Ian Henderson said ambulances had taken the children, aged between 10 and 12, to the hospital's emergency department in a moderate condition.

More than 200 children were in the theatre when St John was first notified at 1.17pm, he said.

1 of 3 JOHN HAWKINS/FAIRFAX NZ Emergency services assist school children out of the Civic Theatre onto Esk Street in Invercargill. 2 of 3 JOHN HAWKINS/FAIRFAX NZ Emergency services assist school children out of the Civic Theatre onto Esk Street in Invercargill. 3 of 3 JOHN HAWKINS/FAIRFAX NZ Emergency services assist school children out of the Civic Theatre onto Esk Street in Invercargill.

Henderson believed it was a medical incident, but he was not sure of its nature. There was no gas or fire involved, he said.

Invercargill Fire Station senior station officer Gordon Rodgers said firefighters checked the theatre and all was clear.

"We didn't find anything. We were almost bystanders," Rodgers said.

BENJAMIN MACK/Stuff.co.nz Emergency services assist school children out of the Civic Theatre in Invercargill

"We just assisted with the evacuation."

Civic Theatre manager Kate Feaver said along with the nine taken to hospital, up to 20 more children were assessed by paramedics at the scene.

Children from St John's, Otatara, New River, James Hargest Junior Campus, Waverley Park, St Theresa's and Waihopai schools were in the theatre when the evacuations began.

Feaver understood most of the children were from St Theresa's School in Invercargill.

"Whether there was a bug going around and some kids were already a bit off colour, I'm not sure," she said.

When phoned for comment, a St Theresa's School staff member refused to put the call through to principal John Lieshout.

"No comment, thanks for calling," she said.

Feaver said all children had been taken back to their schools on buses as a precaution.

Children had fainted while under lights on the stage in previous years, and as a result, staff did not heat the stage area, she said.

The ILT Sing Out show would go ahead from 7pm on Tuesday night, she said.

"We hope all the children who were unwell are feeling better and will be able to join us," she said.

Sing Out musical director Sarah Rae said she had been a director for 25 years and this was the first time she had been involved in an evacuation.

Four ambulances and three fire trucks were on the scene, while police were seen running to the theatre from the Don St police station.

Esk St was blocked off between Kelvin and Deveron streets while the children were being evacuated.

People in white full body suits and masks were draping blankets around the children's shoulders as they left the building.