Two Hong Kong airport security staff were killed when a cargo plane skidded off a runway, hit their patrol vehicle and ploughed into the sea.

Emirates flight EK9788 was arriving from Dubai at about 03:50 local time (19:50 GMT) when it veered off the runway, crashed through perimeter fencing and collided with the security vehicle, pushing it into the water.

The two people inside died. The Boeing 747 ended up partly submerged, but the four crew on board survived.

Officials are investigating the cause of the crash on the north runway. Two other runways remain operational. It's one of the deadliest aviation incidents in years at Hong Kong International Airport, which has a good safety record.

The investigation will focus on the unanswered questions over the path taken by the plane upon landing.

Airport officials have said they gave the correct instructions to the plane and that there are signs on the runway to guide aircraft.

Airport operations executive director Steven Yiu said the patrol car was, at the time, travelling on a road outside of the runway's fencing "at a safe distance from the runway".

The plane then turned away from the runway, crashed through the fencing and collided with the vehicle, pushing it into the sea, Mr Yiu explained.

"Normally the plane is not supposed to turn towards the sea," he said at a news conference hours after the incident, adding that the plane did not send out a distress signal when it was landing.

He stressed that the airport patrol car "definitely did not run out onto the runway".

The weather, runway conditions, the aircraft and its crew will all be looked at as part of the investigation, Mr Yiu said.

Divers managed to locate the bodies of the patrol vehicle?s driver and passenger in the sea.

The two dead ground staff were aged 30 and 41 and had seven and 12 years' experience respectively, officials said. Neither was breathing when recovered from their vehicle, which was five metres (16.4 feet) from the shore, and seven metres under water. The younger of the two was confirmed dead at the scene, and the other later in hospital.

Hong Kong's transport bureau has said it was "saddened" by their deaths and expressed condolences to their families.

In a statement to the BBC, an Emirates spokesperson said the plane "sustained damage on landing in Hong Kong", adding: "Crew are confirmed to be safe and there was no cargo onboard."

It also said the Boeing 747-481 cargo aircraft was wet leased from, and operated by, Turkish carrier Act Airlines. A wet lease is an arrangement where one airline provides the aircraft, crew and insurance to another airline.

The four crew members onboard the plane had opened the emergency doors of the aircraft shortly after the crash. They were spotted by fire service staff who arrived at the scene within two minutes, and were rescued, authorities said.

Pictures show the plane had broken in half, with part of the fuselage submerged in the water with large cracks clearly visible.

At least one emergency evacuation slide deployed successfully.

A police official told the media that criminal investigations would not be ruled out.

An official from the Hong Kong Air Accident Investigation Authority (AAIA) said they were still trying to locate the flight data recorder and cockpit voice recorder - also known as the black boxes - from the sea.

The affected runway would remain closed for the rest of the day, but the airport's other two runways are still in operation.

At least 11 cargo flights initially scheduled to arrive at Hong Kong International Airport on Monday have been cancelled, according to the Airport Authority's website.

It marks the second ever deadly incident at the airport since it moved from Kai Tak to Chek Lap Kok in July 1998.

In August 1999, a China Airlines passenger flight crash landed during a typhoon, killing three people. (CNN)

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