Delta passengers fall sick while waiting on Vegas tarmac in triple-digit temperatures; DOT investigating

The Department of Transportation is investigating after at least one Delta passenger was taken to the hospital for heat-related illness after the plane sat on the tarmac for hours on Monday in Las Vegas, where temperatures reached triple digits.

Passengers on a Delta flight to Atlanta experienced extreme heat while the plane was taxiing at Harry Reid International Airport, resulting in multiple people being treated, according to an eyewitness statement.

Krista Garvin, a field producer for Fox News, was on the Delta flight on Monday, where she tweeted about the "insane experience."

"@Delta what an INSANE experience. First, we were delayed because you did not have a flight attendant," Garvin tweeted. "Then we finally board and sit for almost 3 hours on a hot plane in 111-degree weather. Now we are heading back to the gate cause people are passing out. We are now being told you Can get off but there isn't another flight out to ATL for days. This is actually nuts."

Delta Airlines told ABC News it's investigating the circumstances of why it got so hot in the plane.

"We apologize for the experience our customers had on flight 555 from Las Vegas to Atlanta on July 17, which ultimately resulted in a flight cancelation," the company said in a statement. "Delta teams are looking into the circumstances that led to uncomfortable temperatures inside the cabin and we appreciate the efforts of our people and first responders at Harry Reid International."

Airlines are required to provide comfortable cabin temperatures during tarmac delays, according to the DOT, which announced Thursday it is investigating the incident.

Delta did not immediately respond to requests for comment regarding the DOT investigation.

Passengers have said they were on the plane for at least three hours, while the company said it taxied for over an hour before heading back to the gate. Airlines can be fined up to $27,500 per passenger for tarmac delays over three hours.

Another passenger, April Love, told ABC News that customers were on the tarmac for about three hours and described passengers needing multiple gurneys and oxygen, as well as a flight attendant passing out.

"I saw at least four people getting the oxygen and then I saw at least three gurneys coming," Love said.

The airline was only aware of one passenger needing medical attention.

The flight was canceled following the incident and passengers received compensation.

"[Delta] finally decided to take everyone off because too many people were sick and they want to try and cool down the plane," Garvin said. "Praying they let us back on or we will be stuck here."

Delta reportedly found other flights for customers.

Temperatures at Harry Reid International Airport reached nearly 115 degrees on Monday, according to the National Weather Service.

Dangerous temperatures have been plaguing much of the U.S. for the past month.

The harsh heat that has been blanketing large portions of the South and West for weeks is expected to continue into the foreseeable future, according to forecasts.

Reno, Nevada, tied its all-time high temperature on Sunday at 108 degrees, reaching that number for the first time since 2007. Las Vegas also tied its daily record on Sunday when it reached 116 degrees.

ABC News' Isha Battu, Patrick Doherty and Amanda Maile contributed to this report.