A fire Wednesday morning in Potrero Hill has ended tragically, with one adult victim dead, and firefighters say they had significant challenges fighting the blaze.

The fire broke out before noon at 706 Missouri Street/#3 Turner Terrace — in the lower unit of a multi-unit building in the Potrero Annex housing project. The building is partly below grade, on a slope, and the fire appeared to break out in a lower-level unit.

The cause and origin of the fire is under investigation.

SF Fire Department Captain Jonathan Baxter reported that during the firefight, SFFD rescue crews located and rescued one adult occupant, and that person has since succumbed to their injuries.

Three other individuals were able to self-rescue, Baxter said, and they were uninjured.

Video from the scene, seen above, shows fire trucks lined up above and behind the building, to the rear of its roof, while the fire was blazing out the other (front) side.

"San Francisco Fire was confronted with multiple challenges combatting this fire. This area is very steep with hills, very narrow streets, and lots of overhead wires," Baxter said. "This is one example of how we train and drill daily in areas like this so that when we do get a fire, we're able to access it, we're able to navigate those challenges, and able to get to the fire and extinguish it quickly."

The fire did not extend to any other structures, Baxter said. And as of 1:15 p.m., it was under control.