19 Firefighters Killed in Arizona: Yarnell Hill Wildfire Sparks Deadliest Day Since 9/11 (PHOTO, VIDEO)

19 firefighters have been killed in Arizona, fighting the Yarnell Hill fire, northwest of Phoenix.

The tragic news marks the deadliest day for U.S. firefighters since the 9/11 attacks, and has highlighted the dangers emergency workers are facing as they fight the deadliest wildland fire since 1933, according to the U.S. National Wildfire Coordinating Group.

(Photo: YouTube/Fox News Screen Shot)19 firefighters have been killed in Arizona.

The 19 firefighters who died were part of a specialist squad who work on the frontline against wildfires. Their core mission is to set up barriers to stop the hugely destructive fires from spreading. However, getting into such close proximity to the out of control blazes is extremely dangerous as revealed in this tragic incident.

The firefighters were part of a "hotshot" crew, given the mission to dig a firebreak against the blaze and create an escape route.

State forestry spokesman Art Morrison said, "A hotshot crew are the elite firefighters. They're usually (a) 20-person crew, and they're the ones who actually go in and dig the fire line, cut the brush to make a fuel break. And so they would be as close to the fire as they felt they safely could."

He added, "In normal circumstances, when you're digging fire line, you make sure you have a good escape route, and you have a safety zone set up. Evidently, their safety zone wasn't big enough, and the fire just overtook them."

"Our entire crew was lost," Prescott Fire Chief Dan Fraijo told reporters Sunday night. "We just lost 19 of some of the finest people you'll ever meet. Right now, we're in crisis."

The Yarnell Hill Fire was sparked on Friday, and is believed to have been started by lightening. So far the fire has spread to burn 6,000 acres, and destroyed more than 100 structures, Mike Reichling, incident commander, has said.

Here is a video news report into the incident: