Fire officers have returned this morning to investigate a chemical smell at a Hamilton building where a gas leak put two people in Waikato Hospital last night - and have found the source of the smell.
Station Officer Dave Gunn said a hydraulic drill from a neighbouring premise was leaking.
He described the smell as like "rotten gearbox oil".
Workers at ProPharma have been briefed and are waiting to go back into the building.
Firefighters will now hand over the scene to WorkSafe.