Officials said an investigation would aim to determine what caused the Boeing aircraft to leave the tarmac at Hong Kong International Airport, one of the busiest in the world for air cargo.

The plane's damaged fuselage was left partly submerged in the sea water that borders the airport, with its emergency evacuation slide extended following one of the most serious incidents since the hub 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 onboard.

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

- Abrupt turn -

Yiu said that "weather and runway conditions were safe and meet all conditions for runway operation" at the moment 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 will not rule out launching a criminal investigation.

Helicopters from the Government Flying Service and vessels from the Fire Services Department have been deployed, according to media reports.

Hong Kong began flight operations on its third runway last November, with the city's airport being among the busiest in the world.

The expansion project cost HK$142 billion ($18 billion) and took eight years of construction, with officials saying it would keep the city's airport competitive as an aviation hub.