'The sky was glowing.' Firefighter's harrowing account of the Grenfell Tower fire.

A firefighter among hundreds called to the 24-story Grenfell Tower in West London as it caught fire has shared a harrowing story of being forced to make the most difficult of decisions during the emergency.

That decision: Who to save.

Posting on the Save the UK Fire Service Facebook page, the firefighter, writing anonymously, wrote that they are sharing their story to let people know first responders “did all we could” to save as many lives as possible.

So far, 79 people are believed to be dead or missing in the fire, which began in the early hours of June 14 and lasted more than 24 hours.

"Some things I will miss out as they don't need to be said, some I can't say, other things I will simplify so hopefully everyone can understand them, I'm not looking for praise," the firefighter wrote.

After having been asleep for barely an hour, the firefighter and their colleagues were called to the tragedy.

"We could see this was a bad one immediately. The sky was glowing," they wrote.

"Leaving our truck we started quickly towards it...we are trying to read the conditions in front of us, trying to take in as much information as we could.

"How big is the tower, where is the fire, where is the fire going next, how's it behaving, how many flats are internally affected, how many people are in there?

"We mustered outside the entrance. Parts of the building were already starting to fall down onto the surrounding area.

"As we entered the building the fire on the outside was raging from the top to the bottom.

"Walking up to the bridgehead on the 3rd floor, we were told to look at a floor plan that had been hastily drawn on a wall."

The firefighters were told to rescue five residents stranded in their apartment on the tower's 23rd floor.

The stairwell was so thick with smoke, and the floor numbers so badly marked, that the group became disorientated during the climb.

"Around the 9th floor we lost all visibility and the heat was rising," the firefighter wrote. "Still, we continued up and up through the blackness. We reached what we believed to be the 19/20th floor but there was no way to tell.

"It was here where we found a couple trying to find their way out—panicking, choking, blinded by the thick toxic air."

In less than a minute, the firefighters were forced to make an almost impossible decision: Should they stop their climb and help the couple to safety? Or should they continue on to try and save the five people believed to be stranded on the floors above?

"If we went up another floor would we actually find the 5? If we found them what state would they be in? Could the two of us get that many out especially one or more are unconscious?" the firefighter wrote.

"Am I doing enough? 
Can I give more? 
Am I forgetting any of my training....? Stop....Breath.....Think...."

The group is ordered to escort the couple outside the building. Soon, the female loses consciousness and they meet another fire crew in the stairwell.

"One of them is carrying a little girl," the firefighter noted.

When the crew gets outside, they are "desperate for a drink of water."

Writes the firefighter: "Someone sees us and throws us some water. I drink it straight down. It's gone so fast it barely touches the thirst I have.

"As I look up colleagues are all around us, tunics off their t-shirts soaked through with sweat, no one really able to talk.

"All of us sat there looking at the building we've just come out of. It's worse now! The fire is everywhere and fierce!

"It's hard to comprehend we were just in there."

The firefighter's post also protests the unfair pay for U.K. firefighters, who have been restricted to an annual 1 percent pay raise. The writer says many firefighters have to work second jobs to make ends meet.

And yet, the firefight writes: "We as first responders are still going to be there, we are still going to go out day after day helping the people whose lives are at the lowest point imaginable.

"We are going to be there for you!

"So if you see us out and about please show us your support, show us you're thinking of us and appreciate us by giving us a smile or a wave."