Boston firefighters evacuated hundreds of guests from the DoubleTree hotel in Allston after a generator fire knocked out the building’s power.

Firefighters responded to the 15-story hotel at 400 Soldiers Field Road at 7:20 a.m., according to official tweets.

The fire broke out in a generator room on the second floor, officials said. Electric panels and diesel fuel caught fire, and firefighters worked with building staff to cut the fuel supply.

The hotel was at capacity, and the 400 guests were taken by MBTA buses to the Hyatt Hotel across the Charles River on Memorial Drive, officials said.

The fire cut power to smoke alarms, elevators, hallway and stairway lights, and ventilation systems.

Firefighters went room by room and used master keys to make sure all guests got out safely, officials said.

No injuries were reported.

NStar workers arrived at 9 a.m., after firefighters waited an hour and a half, officials said.

Authorities are inspecting the generator room where the fire broke out and estimated that the blaze caused $200,000 worth of damage.

The hotel’s electrical contractor and building engineer are on scene assessing damage and rerouting power to the hotel, officials said.

Guests will be allowed to return to the hotel once power is restored, officials said.