Guests were escorted out of the conference centre at 12.45am today after the incident started in an employee-only kitchen.
Staffordshire Fire and Rescue Service and West Midlands Ambulance Service attended the scene and two people were assessed.
A WMAS spokesman told the Express & Star: "We were called to reports of a possible chemical incident within an employee-only kitchen area at Alton Towers Hotel at just before 1am this morning. One ambulance, two paramedic officers and the Hazardous Area Response Team (HART) attended the scene.
"Two patients were assessed by ambulance staff and received self care advice before being discharged at the scene."
A fire service spokesman said: "We were called to the Alton Towers Resort following reports of a suspected chemical-related incident within an employee-only kitchen area.
"Crews from Cheadle, Ipstones and Longton attended and carried out an assessment, with specialist equipment, which recorded no readings of any concern. Two people were assessed by West Midlands Ambulance Service and discharged at the scene.
The spokesman added: "Guests were temporarily evacuated as a precautionary measure. Crews later confirmed it was safe for the public to re-enter and advice was given to staff."
Alton Towers Theme Park is closed for the winter season, however, conferences and meetings are still being held in the conference centre.
An Alton Towers spokesman said: “Guests attending an event in our conference centre were temporarily evacuated to the Alton Towers Hotel whilst the emergency services investigated reports of an unusual smell in a staff kitchen area nearby. The all-clear was given shortly afterwards.”