Two airport security staff were killed early Monday after a cargo plane arriving from Dubai skidded off the runway at Hong Kong International Airport, crashing into their patrol vehicle and pushing it into the sea, authorities said.

The Boeing 747 cargo aircraft, operated by Turkish freight carrier ACT Airlines on behalf of Emirates, was attempting to land around 3:50 a.m. local time when it veered off runway 07L, Hong Kong’s north runway, and ended up partially submerged near the airport’s sea wall.

The accident, the city’s deadliest airport incident in more than 25 years, left the patrol vehicle mangled in the water. Both security officers were pulled from the sea unresponsive; one was confirmed dead at the scene, while the other later died in hospital, said Steven Yiu, executive director of airport operations at Airport Authority Hong Kong.

All four crew members on board the plane escaped unharmed, and there was no cargo on the aircraft, Emirates said in a statement. The airline confirmed the flight, EK9788, had “sustained damage on landing in Hong Kong.”

Photos from the scene showed the cargo plane’s fuselage broken in two, with the tail and nose sections separated and an emergency slide deployed.

Authorities are investigating the cause of the crash, including weather conditions, the aircraft’s systems, runway conditions, and possible human error, Yiu said.

Hong Kong’s Civil Aviation Department confirmed that the plane had “deviated from the north runway after landing and ditched into the sea.” Air traffic control recordings reviewed by Reuters indicated the pilot had not reported any technical issues before landing.

Man Ka-chai, chief accident and safety investigator for the Air Accident Investigation Authority, said air traffic control had cleared the flight to land but received no distress call from the pilot.

Yiu said the security patrol car had been operating normally along a service road outside the runway fence. “It definitely didn’t rush onto the runway,” he said, adding that the aircraft “suddenly veered left after landing,” striking the vehicle in what he described as “not a normal path.”

Flights at Hong Kong International Airport were not disrupted, according to the airport authority. Operations continued on the south and central runways, while the north runway remained closed for safety inspections.

The two airport employees who died had worked at the facility for seven and 12 years, respectively. The Airport Authority said it would provide full support to their families.

The crash is Hong Kong’s deadliest airport accident since 1999, when a China Airlines jet crashed while landing, killing three of the 315 people on board.