Update at 11:23 a.m. from Mia Castillo:

Here’s a rundown of those injured in the bus accident, from Paul Pepe at UT Southwestern Medical:

Four of those injured are in critical condition and one is already in surgery because of internal injuries.

Eleven people were taken to Parkland, and 11 others were taken to Baylor Medical Center in Irving.

Others were taken to Las Colinas Medical Center.

Update at 11 a.m., by Matthew Watkins, who spoke to someone on that bus:

Daniel Risik, 73, said he was on the bus with about 35 to 40 who were picked up from a Walmart in Fort Worth and a shopping center in Bedford to take them to the Choctaw Casino in Durant, Okla. He said most of the people on the bus were elderly.

Risik, of Fort Worth, said he believes the bus lost control after a tire blew out.

“We ended up swirling and weaving and then ended up on the side,” he said. “People were screaming and hollering, a very traumatic situation to say the least.”

Most people weren’t wearing seat belts and were tossed throughout the vehicle.

“People were piled on top of each other,” he said. “It was unbelievable. A lady had pinned me. Rescue got there and started pulling people out of a roof emergency hatch. People were hollering, screaming, there was blood all over the place. It was unbelievable.”

Risik said that two people died in the crash.

“There was several other significant injuries, people that were put on stretchers,” he said.

Risik said he wasn’t hurt seriously.

Update at 10:51 a.m., from staff writers Eleanor Sadler (at the scene) and Robert Wilonsky:

The bus was northbound on the turnpike when it went off the right side of the road for unknown reasons, state troopers say.

After striking a rubber crash barrier on the east side of the tollway, it crossed both lanes and struck the concrete barrier in the middle of the highway, pushing it several feet. That’s when it flipped onto the grassy area in the middle of the turnpike, according to Trooper Lonny Haschel.

Haschel says there were a total of 36 people on board and two people were killed. Several others are injured as well.

“We’re in the process of taking witness statements, talking to folks on the bus, trying to determine what happened,” Haschel said, adding that the survivors suffered from “a complete range of injuries … folks that were not injured at all, to cuts and scrapes to internal injuries.”

Parkland spokesman Mike Malaise tells our Eden Stiffman that nine patients have been accepted and they are still assessing their condition. They are still accepting other patients.

Two Dallas Area Rapid Transit buses were also sent to the scene at the request of Dallas Fire-Rescue. Mark Ball, a DART spokesman, says they were sent just after 9 this morning.

“We provide service like this to cities in our service area,” says Ball. “Most often we’re called on to move people dislocated by large fires in multifamily residences, for example. But we’re also asked to keep people warm or cool when called upon.”

When they arrived, the DART buses were essentially turned over to the Department of Public Safety, says Ball, which can use the buses as they see fit — either to shelter or transport victims, in this case.

Update at 10:35 a.m.:

State troopers are now confirming that at least two victims have died in the bus crash this morning.

Many others on board were seriously injured and flown to several area hospitals. The most seriously injured were taken to Parkland Memorial Hospital, which set up a triage area for family.

Here’s more information on the bus company from our Matthew Watkins: Cardinal Coach Line offers tours and charter service from Dallas-Fort Worth to “all points, local or long distance in the United States or Canada,” according to its website.

The company offers tour bus and charter services to groups ranging from 20 to 57 passengers, the website says.

According to a U.S. Department of Transportation database, the company employs seven drivers and uses five busses. Prior to today, the company had not experienced a crash in the past two years. It’s last compliance review was in 2009, when it received a “satisfactory” rating.

Update at 10:20 a.m.:

Witnesses say victims may still be pinned under the bus, and several media outlets are reporting that two people were killed in the roll-over crash.

The Dallas County medical examiner’s office was called to the scene, though officials there are not confirming deaths.

DFW Scanner reports via Twitter, “Command is advising 16 patients in critical condition.”

Many of those on board the bus were described as older folks, on their way to Choctaw Casino Resort across the border in Oklahoma.

NBC-Channel 5 is reporting that at least 40 people were on the bus. Witnesses are telling several media outlets that the passengers, most of whom were elderly, were not wearing seat belts.

As noted below, it appears they were headed to Choctaw Casino Resort in Durant, Oklahoma.

Parkland, one of the hospitals to which victims will be taken, is at code yellow.

Original item at 9:38 a.m.: Emergency crews, including all available ambulances in the area, have been called to an enormous accident northbound State Highway 161 and Belt Line Rd. According to initial reports, including KXAS-Channel 5, a charter bus turned over, and as many as 40 people may be trapped. Firefighters and police officers are still in the bus trying to rescue passengers.

The live video above shows rescue workers transporting the injured to red blankets, where they’re being treated before being transported to the hospital via CareFlight helicopters and ambulance. The injured are being taken to Baylor University Medical Center at Dallas, Parkland Hospital and Methodist Dallas Medical Center.

WFAA-Channel 8 is reporting that one person is trapped under the bus, and that “a multitude of the injured are elderly.”

DFW Scanner is reporting that is being labeled “a mass casualty incident.”

All lanes of S.H. 161/President George Bush Turnpike between Belt Line and the tollbooth are shut down.

Jon Sasser, an executive producer at WFAA-Channel 8, is reporting that the charter bus is from Cardinal Coach Line based out of Mansfield. Our calls to Cardinal have gone unanswered.

A victim on the bus tells Channel 5 they were on their way to Choctaw Casino Resort.