Two people have been taken to Waikato Hospital in a serious condition, after an incident with a gas heater in Ngaruawahia.

Emergency services were called to the house on Kia Toa Street at around 2 o'clock.

The ambulance service says people were treated for smoke inhalation, after both an open brazier and a gas heater were being used inside.

Two other people were also taken to hospital, one in a moderate condition and another with minor injuries.