Emergency services rushed to the Sheraton Grand Hotel and Spa at around 1pm yesterday, following reports of an incident on the third floor.
Visitors scrambled to bars surrounding Festival Square until the hotel – which boasts 269 guest rooms and the renowned One Spa – was declared safe.
A small number of staff were treated at the scene after breathing in fumes from a substance that had been used by cleaners to decontaminate one of the bedrooms.
According to hotel officials, the cleaning products had been hired from a third-party supplier for a one-off deep clean.
Guests were allowed back into the restaurant and spa shortly after the evacuation, but were not given access to rooms until a few hours later.
Donna Carlson, 68, from Canada, was in her room getting ready to head out when she realised something was wrong.
She said: “My friends and I were just in our rooms when all the alarms started going off.
“We began to panic as we had no idea what was going on, we had been having such a lovely time.
“When we started to make our way downstairs, we noticed everyone was leaving the hotel but nobody would tell us what was going on. It was very alarming.”
She added: “When we got outside, one of the paramedics told us it was something to do with chemicals.”
As well as the Scottish Fire and Rescue Service, Police Scotland and the Scottish Ambulance Service were also in attendance.
Some guests faced a waiting time of up to two hours before they could check back in to the hotel.
A spokeswoman for the Sheraton Grand Hotel and Spa insisted that the safety of guests was “paramount” and hotel officials would work with each individual affected on a case-by-case basis.
She said: “Guests were evacuated yesterday afternoon. It was due to an incident with cleaning products, which caused non-toxic fumes.
“The hotel team worked diligently with the local fire brigade to resolve the issue as quickly as possible.”
A spokeswoman for the Scottish Fire and Rescue Service said: “We attended the Sheraton Hotel yesterday afternoon following reports of a chemical incident in one of the rooms.
“On arrival, the ambulance service were there and were dealing with a number of casualties who had become unwell after inhaling an unknown chemical.
“A full evacuation of the hotel then took place.
“It is believed the chemical was a fogging agent that was used to decontaminate one of the rooms.”