The 911 system in Dallas went down for about 22 minutes on Thursday night.
City spokesman Frank Librio said in a statement that the system went down at about 7:33 p.m. because of maintenance on the HVAC for the phone systems at City Hall.
The 911 call center is in the basement of City Hall.
"During a 22-minute period, incoming calls would have been picked up by other city towers," Librio said.
The backup system at the fire training academy was activated at 7:55 p.m.
Dallas Fire-Rescue deployed fire engines to assist with any emergency needs. Crews patrolling in West Dallas found a fire at 2425 Bickers Street. Firefighters quickly put out the fire, but some damage was reported to at least one apartment.
The city said it did not know of any major incidents while the 911 system was down.
During the outage, people were not able to call 911 from landlines. It was not immediately clear if cellphone calls were also affected.