One worker at the Hyatt Regency in downtown Bethesda was injured and 400 guests were evacuated early Monday when a fire broke out in the electrical room, according to the Montgomery County fire department.

The injured person is a contractor who was driven by a colleague to an area hospital and later was taken to a burn center facility, said Montgomery County Assistant Fire Chief Scott Graham, a fire department spokesman. Graham termed his injuries serious but not life-threatening.

The guests were taken by bus to Bethesda-Chevy Chase High School. Once they arrived, police and Red Cross officials created a manifest of which guests had essential items — such as medication — in their rooms. After the fire was out, these guests were escorted back to their hotel rooms to get those essential belongings, Graham said.

The guests were put up in other hotels. Some of them, who were to check out Monday morning, were able to go on their way, said Graham.

The cause of the fire remains under investigation, but officials said a worker in the electrical room heard a loud bang.