Around 400 people were evacuated from the hotel on Portman Square to a neighbouring hotel after the blast in the hotel basement. Initially it was reported that 12 people were injured, but the figure was later revised to 14. Five of the injured were taken to hospital.
The London Fire Brigade said the explosion has caused "extensive damage to the basement and ground floor". Five cars in a nearby street were also damaged.
Six fire engines and 35 firefighters attended the scene, alongside a dangerous structures engineer and the gas authorities.
The cause of the explosion is being investigated, but it is believed to have been caused by a suspected gas leak.
In a statement, Hyatt said the group's priority is the "safety and wellbeing" of its guests and staff. "We are currently working to provide guests with accommodations while we evaluate whether the hotel received any significant damage."
The Hyatt Regency is the home of the restaurant Locanda Locatelli, run by Giorgio Locatelli.
The general manager of the hotel and area director UK & Ireland Hyatt is Michael Gray, who was named The Caterer's Hotelier of the Year in 2007.