A cargo plane involved in a fatal collision at the Hong Kong International Airport on Monday had landed successfully on the north runway in clear weather conditions before suddenly veering off track and crashing into the water, authorities said, amid a hunt for the flight recorders that may shed light on the cause of the deadly accident.

Emirates cargo flight EK9788 – flying in from Dubai – had landed shortly after 3.50am and had travelled halfway down the runway before it suddenly turned to the left and collided with a security patrol vehicle, pushing it into the sea, officials told a press conference.

The airliner – a Boeing 747 cargo aircraft – broke into two and also fell into the water. Firefighters responded quickly to the incident, and rescued the four air crew who were waiting by the door.

However, it took divers some 40 minutes to locate the car, which was submerged some seven metres underwater.

A 30-year-old passenger was declared dead at the scene, while the driver, 41, was pulled from the vehicle unconscious and unresponsive, with a head wound. He was certified dead later in hospital.

The four air crew were unharmed.

"We are deeply saddened and extend our deepest condolences. We will provide their families with all necessary support and assistance," said Airport Authority executive director Steven Yiu.

He said the north runway will remain shut for the time being as investigations are conducted, but the more than 1,000 flights scheduled for Monday are expected to continue unaffected.

"The south and centre runways are operational. We do not expect any impact to today's operations," he said.

"According to information we have [of] that moment, weather and runway conditions were safe and met all conditions for runway operations. An investigation is continuing. The north runway remains closed. It'll be reopened after the safety assessment."

The Air Accident Investigation Authority is now searching for the plane’s flight recorders to help with its probe into the accident, according to chief accident and safety investigator Man Ka-chai.

"We will look into various aspects, including the aircraft's system, its maintenance, its operation, the weather, and runway conditions, to determine what caused the accident," Mak said. "We are currently searching for two 'black boxes' – the flight recorder and the cockpit voice recorder".

The Civil Aviation Department, meanwhile, said the aircraft did not ask for any help before it skidded off the runway.

The Transport and Logistics Bureau expressed concern over the accident, with a spokesperson saying authorities are "saddened by the loss of the two ground staff members".

"The Air Accident Investigation Authority will actively investigate the cause of the accident, while the Civil Aviation Department and the Airport Authority Hong Kong will fully cooperate to ensure the safety of airport operations," it said in a statement.