An engineer said on Friday that preparations alone for the removal of an Emirates cargo plane that veered off course at the start of this week - and ended up in the sea - would take at least two days.

The Boeing 747 freighter crashed into a patrol vehicle, nudging it into the sea and killing two security workers inside in the early hours of Monday.

Louis Szeto, former chairman of the mechanical, marine, naval architecture and chemical division at the Hong Kong Institution of Engineers, told an RTHK radio show that the salvage crew has to ensure that no fuel remains on the aircraft to prevent leakage.

He said the amount of time needed for the removal after stabilising what remains of the aircraft would depend on various factors.

"As to when the salvage work can begin, it will depend on the weather – whether there is monsoon wind and the situation of tide phases – so as to fix the position of the salvage vessels," he said.

Szeto said divers have to be deployed before the plane can be lifted to help map the extent of the damage to the aircraft and understand how it is sitting beneath the surface, such as whether the plane is partially or fully broken into half.

He believes the aircraft will be placed on shore after being lifted from the water before it is transported to a maintenance centre for further investigations.

On the same show, Warren Chim, deputy chairman of the institution's aircraft division, said international standards stipulate the submission of a preliminary incident report within 30 days, with a final report to follow in a year's time.

The salvage operation on the side of the north runway, where the plane landed before veering off into the sea, began on Thursday. The airport's operations remain unaffected, with flights diverted to the other two runways.

The Airport Authority said the north runway can reopen to air traffic within three hours, as soon as the two salvage vessels move away from the restricted waters.