Two Hong Kong airport security staff were killed early on Monday after a cargo plane from Dubai skidded off the runway on landing, collided with their security patrol vehicle and pushed it into the sea, the city’s airport operator said.

The Boeing involved in the deadliest airport incident in the financial hub in more than 25 years also fell into the water and was partially submerged, but all four crew members on board escaped.

The airport security staff were not breathing when rescued from the water, with one confirmed dead at the scene and another later at hospital, said Steven Yiu, executive director of airport operations at Airport Authority Hong Kong.

The accident at the world’s busiest cargo airport involved a plane operated by Turkish freight carrier ACT Airlines on behalf of Emirates, the Dubai-based airline said in a statement.

Authorities are still investigating the exact cause of the crash, with weather, runway conditions, the aircraft and aircrew part of the investigation, Yiu said.

The accident occurred around 3:50 a.m. Hong Kong time on Monday (1950 GMT on Sunday).

An air traffic control recording available on LiveATC.net reviewed by Reuters indicated the cargo plane’s pilot confirmed plans to land on runway 07L where the crash occurred, but he did not report any technical issues on the recording.

“An incident happened at the airfield just now,” a female controller said minutes later.

Man Ka-chai, chief accident and safety investigator for Hong Kong’s Air Accident Investigation Authority, confirmed air traffic control had directed the flight to land at the north runway, but added: “We didn’t receive any message requesting help from the pilot.”

Yiu said the security patrol car was in charge of patrolling the north runway along a road that was outside the runway fence. It was operating in its usual area and “definitely didn’t rush onto the runway,” he said.

The airplane suddenly veered left after landing on the runway before hitting the car, which “wasn’t a normal path”, he said.

Airport flights not affected

Flights at Hong Kong’s airport have not been affected, Yiu said, adding that the northern runway at the world’s busiest cargo airport, where the incident occurred, would reopen after safety inspections were complete.

The south and central runways are operating as normal, the authority said.

Photos taken after the accident showed a cargo aircraft with AirACT livery partially submerged in water near the airport’s sea wall with an escape slide deployed and the nose and tail sections separated.

Hong Kong’s Civil Aviation Department said in a statement on Monday that the aircraft had “deviated from the north runway after landing and ditched into the sea.”

Emirates said flight EK9788 sustained damage on landing in Hong Kong on Monday and was a Boeing 747 cargo aircraft wet-leased from and operated by ACT Airlines.

“Crew are confirmed to be safe and there was no cargo onboard,” Emirates said.

Boeing did not immediately respond to a request for comment.

ACT Airlines is a Turkish carrier that provides extra cargo capacity to major airlines. It did not respond immediately to a request for comment outside normal business hours.

Flight tracking service FlightRadar24 said the aircraft involved in the accident was 32 years old and had served as a passenger plane before being converted into a freighter.

Yiu said the airport authority would provide all necessary assistance and support to the family, adding the two staff who died had worked at the airport for seven and 12 years respectively.

It was the deadliest airport accident in Hong Kong since a China Airlines flight crashed on landing in 1999, killing three of the 315 people on board, according to an Aviation Safety Network database.