An explosion at the Hartsfield-Jackson International Airport in Atlanta on Tuesday, which led to minor flight delays, was likely caused by a malfunctioning power supply unit, airport officials said, according to Associated Press.

A portion of concourse D was evacuated after a maintenance shed near Gate D 21 exploded on Tuesday.

The blast happened at around 8.40 a.m. EDT when a unit supplying power to the air-conditioning system to concourse D malfunctioned, airport spokesman Reese McCranie was quoted as saying by AP.

Atlanta fire department was called to the scene and all 36 gates of Concourse D were evacuated as a safety precaution. Power was restored by 11 a.m. and there was no fire. None of the passengers were injured, but the airport explosion caused minor property damage.

Passengers were soon allowed to return to their gates and about 35 flights were delayed by an average of 30 minutes, McCranie told AP.

Atlanta airport officials said that a malfunction in an electrical circuit box triggered the explosion and it was not set off by a person. FBI Special Agent Stephen Emmett too clarified that the airport explosion did not seem to be related to terrorism, CNN reported.

Separately, two bomb threats led to evacuations in five state buildings in downtown Atlanta on Tuesday morning. Georgia State Patrol officials told that an anonymous caller tipped off a bomb threat to the Health Building located at 47 Trinity Avenue, near the Georgia State Capitol.

Four other buildings were also evacuated due to their proximity to 47 Trinity Avenue and employees housed in these buildings were given the all-clear sign to return to work by 11 a.m. The Capitol was not evacuated.