Firefighters put San Francisco’s auxiliary water system into use during Tuesday inferno

Fire crews worked overnight and in to Wednesday putting out hotspots at the scene of a huge fire that broke out Tuesday morning in San Francisco's South of Market neighborhood.

Crews say they have a lot of work that still needs to be done before they can clear the scene.

Fire crews have been working for more than a day containing hot spots after a massive fire swept through six buildings Tuesday morning, some of those buildings burned to the ground.

Crews say the sheer scope of the scene made this a challenging fire.

"We have hotspots similar to what we had on the Pier 45 fire on Memorial Day," said Lt. Jonathan Baxter from the San Francisco Fire Department. "Where this is a large area, almost equivalent to one square city block."

The fire department says the warehouse style buildings that the fire consumed pancaked on top of themselves, creating areas that can flare up over and over again.

Crews will have to continue to work on those hot spots before they can bring in heavy machinery to move the debris around, and get investigators through the entire scene to determine the cause.

Investigators are already beginning their work, including following up on whether this massive fire could be connected to a small mattress fire that crews responded to in the same spot one night before.

"Our fire investigation task force was called to that incident and was on scene for an extended period of time investigating that incident, which is still under investigation, and assuring that there was no extension from that fire and that that fire was completely out," said Baxter.

Fire crews aren't releasing much information about the three residents they report were displaced from this largely commercial and industrial area, saying only that they are making sure they get the services they need.

"It's not up to us to determine, nor are we going to determine if that's a legitimate traditional living space or not," said Baxter. "We will work with our partners at Department of Building Inspection and our fire prevention bureau at a later time. Our priority is making sure those people are taken care of."

The fire dept says drills and teamwork with other city agencies helped them marshall the resources they needed, specifically sourcing enough water, to battle massive fires like the one on Tuesday.

They say they're also working on an after-action report to see what worked and what didn't to improve their response for the next time they encounter a similar situation.