An operation to salvage the deadly bus wreck from a ravine in Genting Highlands will continue tomorrow as two heavy-duty cranes needed for the exercise are expected to arrive at the site at about 8pm tonight.

Bentong police chief Supt Mohd Mansor Mohd Nor said the cranes could only climbed uphill at 5km per hour and the operation would only resume tomorrow morning due to safety factor.

The operation stopped about 2.30pm today, he told reporters here.

Although a heavy-duty crane was already deployed at the site, it was insufficient to retrieve the bus wreck.

The bus plunged about 60 meters into a deep ravine yesterday while travelling downhill at KM3.5 Jalan Genting Highlands, killing 37 people, including the driver, and injuring 16 passengers, making it the worst bus mishap in the country.

Meanwhile, the Malaysian Institute of Road Safety Research Malaysia (Miros) deployed an unmanned aerial vehicle (UAV) to help determine the cause of the accident.

It was flown twice for about 15 minutes from 9am and 10.15am along the route plied by the bus from the peak of Genting Highlands to the crash site covering a distance of 3.4km.

UAV pilot Fhirdaus Shamsuddin, who operated the UAV, said the German-made UAV quadcopter, which was one of two UAVs bought by Miros two years ago, was equipped a GoPro digital camera and a global positioning system (GPS).

"We took pictures along the bus route, the crash site and the position of the ill-fated bus from the unmanned flight," he told Bernama at the crash site.

Fhirdaus, 26, flew the UAV from a mobile-control unit fixed to a four-wheel drive vehicle which beamed a liquid crystal display (LCD) images taken by the GoPro camera.

He said Miros had so far deployed the UAV to probe 15 accidents but the bus tragedy near the highland resort yesterday remained he worst accident so far.