Just before midnight Saturday, a Tesla drove swiftly around a curve, veered off the road, struck a tree and burst into flames in The Woodlands, Tex., a suburb north of Houston, police said.

It took four hours for fire officials to put out the flames. Inside the 2019 Model S, police said, they found two passengers dead — and discovered that neither was driving the Tesla at the time of the crash.

“Our investigation has determined that one of the victims was in the front passenger seat; one was in the back seat,” Mark Herman, a constable for Harris County Precinct 4, told KHOU, adding police were “100 percent certain that no one was in the driver’s seat.”

Tesla has pushed ahead with technology it terms self-driving, increasing the driver assistance capabilities in some of its cars last fall despite criticism from some safety regulators who questioned whether the technology had been sufficiently tested. Tesla CEO Elon Musk said in a tweet Monday that data recovered “so far” indicated the car’s Autopilot function was not enabled, and the owner did not purchase the most advanced driver assistance suite that Tesla calls “Full Self-Driving.”

That disclosure, which came independent of federal investigators, raised new questions in the crash, including how much data Tesla had been able to recoup and whether it had been independently reviewed at the time of Musk’s statement. The National Transportation Safety Board, which sent two investigators to Texas to probe the crash, did not immediately respond to a request for comment.

The NTSB said it would look into the vehicle’s “operation” and the fire after the crash. It was unclear whether Musk’s disclosure about Autopilot was authorized by federal investigators.

In a previous case, however, the NTSB booted Tesla as a party to its probe into a fatal crash in California after the company released investigative findings ahead of the federal authorities.

The National Highway Traffic Safety Administration also said it was investigating Saturday’s crash. Altogether, the safety body has initiated 28 investigations into Tesla crashes, a spokeswoman said.

Although some Tesla vehicles can steer, accelerate and brake on their own in certain circumstances, drivers are still required to supervise and be ready to intervene. But as the autopilot features have become more common, some distracted drivers have been in crashes as their cars navigate on their own.

The driver of a 2017 Tesla model X SUV died after he crashed on Highway 101 in Mountain View, Calif., in March 2018. In the minutes leading up to the collision, the driver had been accessing a video game on his phone. Another driver died in a 2016 crash in Williston, Fla., after a tractor-trailer pulled out in front of the Tesla. The car’s autopilot feature failed to brake because it did not register the truck’s white side against a brightly lit sky. Investigators concluded the driver should have had an opportunity to brake before the collision, but was probably distracted. The National Highway Traffic Safety Administration found no faults with the Tesla’s autopilot software.

Officials haven’t confirmed that the passengers who died on Saturday were using Autopilot. The New York Times reported their wives had heard them discussing that feature before leaving that night.

Saturday’s crash also highlighted another concern about the electric cars that has been on regulators’ radar in recent years: hard-to-extinguish fires.

Officials in Houston said the battery inside Tesla ignited after the collision, causing a fire that burned for four hours and required more than 30,000 gallons of water to put out.

“Our office has never experienced a crash scene like this,” Herman told KHOU. “Normally, when the fire department arrives, they have a vehicle fire under control in minutes, but this went on for hours.”

Video footage from the crash scene captured by KHOU showed the vehicle’s smoldering frame, with nearly all of its exterior and interior structures destroyed by the fire.

The National Transportation Safety Board last year published an independent review of the risk of fires caused by the lithium-ion batteries used in electric vehicles. The board found that if a collision damages a battery, there is a risk of “uncontrolled increases in temperature and pressure, known as thermal runaway, which can lead to venting and combustion of toxic gases, cell rupture and release of projectiles, and battery reignition/fire.”

Regulators reviewed fires caused by the batteries in several Tesla vehicles, according to an NTSB report.

In 2017, a driver lost control of a 2016 Tesla model X SUV and crashed into the garage of a house, according to the report. The battery caught fire, which spread to the building. About 45 minutes after firefighters put the initial flames out, the battery flared up again in a “'blowtorch' manner” and it took several hours to quell the fire enough to move the vehicle.

A 2014 Tesla model S burned for more than an hour after crashing in Fort Lauderdale, Fla., on May 8, 2018. Firefighters struggled to put the flames out as the battery continued to smolder, even after hundreds of gallons of water had been sprayed onto the blaze. Two people died in the crash and a third passenger was seriously injured.

In June 2018, in West Hollywood, Calif., a 2012 Tesla model S appeared to spontaneously catch fire as it was being driven, according to the report. No one was injured in that incident.

The report also noted that the batteries used in electric vehicles designed by different companies also carried a risk of fire.

Tesla did not immediately return a request for comment late Sunday on the crash in Texas. Musk tweeted about the safety of the company’s autopilot features Saturday afternoon.

“Tesla with Autopilot engaged now approaching 10 times lower chance of accident than average vehicle,” he said, while also sharing a link to the company’s most recent safety report.

According to that report, Tesla’s car batteries are designed to prevent fires following collisions.

“[I]n the extremely unlikely event that a fire occurs, the state-of-the-art design of our battery packs ensures that its safety system works as intended and isolates a fire to select areas within the battery while simultaneously venting heat away from the passenger cabin and the vehicle,” the report said.