Needless to say, this will alert the rest of the soldiers and you'll have a full-fledged firefight on your hands. Try to take out the men on the far side of the room with grenades or fire/napalm arrows before they get too close. If any of the men do manage to flank Lara, you can use the shotgun and/or Dodge Counter maneuvers to deal with them.
If you don't drop the generator at the beginning, there will be a few extra enemies to deal with, but you can also use the fuel barrel against them.
Shooting the barrel causes the generator to explode as well, killing anyone standing nearby. (NOTE: Lara's injuries in this picture above weren't caused by the explosion but by another guy who sneaked up from the side and shot at her while I was trying to get the screenshot. It won't hurt you if you're this far back.)
There are a couple of demolitions men among the crew, and some of the others have Molotov cocktails. When they throw explosives at you, scramble out of the way and take cover in a different place. There are several low walls and columns, though these will eventually be destroyed by enemy bullets. The two piles of metal pipes are solid and reliable, though.
During the fight, more men will slide down ropes from the upper levels. You may be able to shoot some of them off the lines as they descend.
When you've taken out the rest of the men, a lone guy with a machete and metal shield shows up. He lumbers slowly across the room, giving you plenty of time to get ready for him. Move out from cover so you have room to maneuver. Then take him out using the Dodge Counter/Dodge Kill maneuver.
Keep your weapon drawn by holding the Aim button as you wait for the enemy to get close. When he lunges at Lara, continue to hold Aim to keep your weapon trained on him. Then press Dodge/Roll while moving to either side.
If your dodge is successful, the Melee icon appears on screen, just like in the quick time events. Press Melee in time with the prompt (i.e., wait for the gray circle to to contract into the inner ring and the Melee icon to appear, then press the button).
The Dodge Counter icon flashes briefly on screen, as shown above.
Lara takes over. If you have the Dodge Kill skill unlocked, she'll stab the guy in the neck with an arrow, killing him instantly. If you have Dodge Counter but not Dodge Kill, she'll stab him in the leg with an arrow, leaving him vulnerable for a gunshot or Melee finisher. If you don't have either of these skills yet, he should still lose his balance temporarily when you dodge, exposing his back so you can shoot him. You'll then need to repeat the process to finish him off.