Ten people have been treated for breathing difficulty following an incident at the Loftus Leisure Centre in East Cleveland, emergency services say.
Six of the 10 were taken to hospital on Tuesday following the afternoon's incident.
North East Ambulance Service said: "We treated 10 patients with breathing difficulties and we transferred six of them to James Cook and North Tees hospitals.
"We had three paramedic ambulances, three hazardous area response team crews and two officers"
A South Tees Hospitals NHS Foundation Trust spokesperson said: “Seven casualties were brought to The James Cook University Hospital including a member of the emergency services who was subsequently discharged. Of the remaining six casualties, five are comfortable and one is stable.”
The leisure centre remains closed until further notice. Peter Smith, contract manager, said:
“Loftus Leisure Centre was evacuated yesterday afternoon due to a gas leak in the spa. The emergency services were called and we can confirm individuals were taken to hospital.
“The building remains closed until further notice and investigations are underway. We are unable to provide any further detail at this stage, but we will keep our customers informed accordingly.”