Laclede Gas, the Melville Fire Protection District, and Sunset Hills Police Department responded to the Hampton Inn at Lindbergh Boulevard amid reports of a carbon monoxide leak.
Three hotel guests were alerted of the leak after spending time in the pool area.
At around 7 p.m., emergency crews were working to ventilate the hotel with large electric fans. Officials at the scene say 30 people were evacuated.
"Any room that we didn't get an answer we went into so we could make sure everything was evacuated," said Deputy Chief Tim Dempsey with the Melville Fire Protection District.
In a tweet Friday night, Laclede Gas wrote the building was safe.