Officials said an investigation would aim to determine what caused the Boeing aircraft to leave the tarmac at Hong Kong International Airport, the world's busiest for cargo last year, according to an industry ranking.

The plane's damaged fuselage was left partly submerged in the seawater that borders the airport, with its emergency evacuation slides extended, following one of the most serious incidents since the airport began operations in 1998.

Steven Yiu, executive director of airport operations at Airport Authority Hong Kong, said the cargo plane from Dubai "went off from the north runway upon landing and crashed through the fence and into the sea" at around 4 am (2000 GMT Sunday).

Yiu said the patrol car was not on the runway at the time of the accident, and that "it was the aircraft that veered off the runway to hit the patrol car, which was outside the fence" and pushed it into the water.

A 30-year-old man aboard the ground vehicle was confirmed dead at the scene while another, aged 41, died after being rushed to hospital.

Both men were retrieved from the sunken car by divers around five metres (16 feet) from the shore.

Emirates airlines said the plane's crew were confirmed to be safe and there was no cargo on board.

Emirates added the involved plane was on a temporary short-term, or "wet", lease from the Istanbul-headquartered Act Airlines, which operated the aircraft.

- Abrupt turn -

Hong Kong's airport handled 4.9 million tonnes of cargo in 2024 and was ranked the world's busiest cargo airport by Airports Council International (ACI) World in April.

Monday's incident happened at the airport's northernmost and newest runway, part of a HK$142 billion ($18 billion) expansion project that was completed last year.

The cargo plane's visibly cracked fuselage was seen floating on the water with its green tail section torn off, according to an AFP reporter at the scene.

Police patrol boats moved around the wreckage as authorities used cranes and tow trucks to search for the aircraft's "black box", which contains recording devices that may shed light on how the incident occurred.

Yiu said that "weather and runway conditions were safe and meet all conditions for runway operation" at the time of the incident.

Officials provided a diagram that showed the plane abruptly turning left halfway down the length of the runway.

The aircraft did not send an emergency signal and gave no reply when radioed by the airport, officials added.

The airport's north runway was temporarily closed on Monday, while the other two runways remained operational.

The incident was not expected to impact airport operations, Yiu said.

A spokesman for the Transport and Logistics Bureau expressed deep concern over the incident, adding that the Air Accident Investigation Authority will "actively investigate the cause of the accident".

Police said they would not rule out launching a criminal investigation.