An early morning fire in a Tenderloin apartment building set off an explosion that prompted a neighbor to enter the building and alert residents. 

The fire occurred just before 6 a.m. at 424 Ellis St. and caused no injuries, but it’s still unknown whether anyone was displaced from the blaze, according to the San Francisco Fire Department’s Twitter account.  

JJ Smith, who lives near the residence and filmed the fire, said he was visiting a friend when he heard “a loud boom” that prompted him to begin knocking on doors and urging people to evacuate.

A video that Smith posted to Twitter shows the building’s custodian attempting to kick down a locked door as smoke billowed from its cracks. They feared that a man named Franky was still inside but later discovered that Franky had made it out safely, Smith told The Standard.  

“I’m out of breath,” Smith said, as he and the custodian gasped for air while smoke filled the hallways and the fire alarm blared. 

“Let’s get the fire department. Get out Mike. Get out. Go out,” he wheezed before fumbling with the doorknob of the fire escape. 

Another video by Smith shows the flames filling a top-floor corner apartment as black smoke pours out from both sides of the building.  

The fire department said that the blaze is still under investigation. The San Francisco Police Department has been contacted for comment.