Calvin Harris' House Catches Fire in Los Angeles, Major Response

5:00 PM PT -- Photos from the fire at Calvin Harris' Los Angeles estate show some of the structure damage ... and a patched-up roof.

Check out the pic, you can see the section of roof firefighters had to cut out to get closer to the blaze and extinguish the flames.

What a mess!!!

Calvin Harris' Los Angeles home partially caught on fire this week -- and it sounds like firefighters sent the whole cavalry at first ... responding like this was a 5-alarm blaze.

Law enforcement sources tell TMZ ... multiple fire engines rushed to the DJ's Beverly Hills mansion Wednesday night, with firefighters arriving at his 3-story home in the area -- where reports came in of a possible fire on one of the upper floors.

We're told the call came in around 8:25 PM, with the reporting party saying there was the smell of smoke coming from inside the home. At first, there was an obvious and major reaction to this -- because LAFD sent up to 10 different fire units, and at least 20 different responders.

Eyewitnesses on the scene tell TMZ ... that there was a mix of multiple fire trucks and ambulances -- and that there were even helicopters swarming to tend to this. One eyewitness tells us smoke was clearly visible and rising from the roof of CH's house.

Now, luckily, this ended up not being nearly as dangerous as was initially suspected -- our sources tell us firefighters showed up and ended up ascertaining that the fire was coming from the third floor of the house ... near the theater room, we're told.

In order to access the void space -- meaning an area that isn't out in plain view -- firefighters had to cut through the second-story roof to get access to a wall inside, where the fire was actually taking place. Our sources say there were flames near an HVAC system there.

All in all, we're told this appeared to be an electrical mishap ... and it took them about 52 minutes to extinguish the fire. Our sources say there appears to be about $100,000 in damage -- but in the end, they were able to put it out and nobody was harmed.

Worth noting, Calvin himself was not home. In fact, he doesn't live there right now. Sources close to CH tell TMZ that Calvin's been leasing this pad of his for at least a few years now.

Either way ... rough week for Cal, no doubt. First, he had the Taylor (non)run-in at the Grammys -- and now, his crib ended up lighting up the whole block with a fire.

This is NOT what he came for! 😅