The search, involving U.S., Indian and Nepali military choppers and a battalion of 400 Nepali soldiers, has been joined by two MV-22B Osprey, a tilt-rotor aircraft capable of taking off and landing vertically.
Military helicopters flew over eastern Nepal and a team sent up a drone on Thursday to search for a missing U.S. Marines Huey chopper, as the death toll rose from the Himalayan country's second big earthquake in less than three weeks.
A Reuters correspondent flew on a Nepali military helicopter along the Tamakoshi river that runs by the town of Charikot, in the mountainous Dolakha district worst hit by Tuesday's 7.3 magnitude quake that killed nearly 100 people.
The river winds through rugged Himalayan terrain in an area whose tallest peak soars over 7,000 metres (23,000 ft). Hillsides are cloaked with dense forest that would make it hard to sight the chopper that went missing after the crew was heard over the radio saying the aircraft had a fuel problem.
In Koshikhet village, a U.S. civilian team was using a drone to search for the missing Marine Corps UH-1Y, or Huey as the model is better known, which was carrying six Marines and two Nepali soldiers.
"We are using infrared vision to look for hotspots and any signs of life," said drone operator Shepherd Eaton, from GlobalMedic, a U.S. aid agency that specialises in search and rescue.
The search, involving U.S., Indian and Nepali military choppers and a battalion of 400 Nepali soldiers, has been joined by two MV-22B Osprey, a tilt-rotor aircraft capable of taking off and landing vertically.
So far, no sign has been found of the Huey, which was on an aid mission in Dolakha district near Tibet when it lost contact on Tuesday.
"We are still trying to locate it. There is no evidence to prove that it has crashed," said Marines spokeswoman Captain Cassandra Gesecki.
The Huey was kitted out with a satellite location device, a radio and an emergency beacon. It may have come down in a "dead zone" for radio signals, though, making it hard for searchers to locate it.
"If it just landed in that forest, it would be lost," said Bala Nanda Sharma, a retired Nepali army general, gesturing to a hillside from the Charikot army base from which helicopters were flying.
The death toll from Tuesday's tremor reached 91, Nepal's home ministry said on Thursday.
Another 2,428 people were injured in the quake, which struck 17 days after a huge earthquake killed more than 8,000 people and damaged or destroyed hundreds of thousands of buildings in the impoverished Himalayan nation.
SECOND QUAKE ADDS TO PAIN
Prime Minister Sushil Koirala, visiting Dolakha district, said massive landslides made relief work difficult. "Still, we are fighting," he said.
Koirala gave up his seat on his helicopter so that a woman with critical head injuries could be evacuated from Charikot to Kathmandu. He only flew back to the capital when it returned.
Medecins Sans Frontieres emergency coordinator Dan Sermand said Tuesday's tremors caused serious damage to buildings in remote areas that had already been weakened.
"The first has done quite some damage. The second has finished the job," Sermand said by telephone from Kathmandu.
MSF deployed two helicopters, each with two medical teams, to Dolakha to stabilize and evacuate the injured. Civilian helicopters were not asked to join the search for the missing U.S. chopper.
Home Ministry official Laxmi Prasad Dahal said on Wednesday he feared the search was diverting resources from relief and rescue operations.
Relief workers and aid were only slowly reaching remote areas, where many roads have been cut by landslides - including the single-track road along the Tamakoshi river where no moving vehicles could be seen from the air.
In Mabu village, the Nepali search helicopter stopped to find out if the locals there had any information about the missing helicopter.
"You are the only person we have seen so far," said Bhagawat Gurung, 18, a villager, when asked whether any aid workers had reached them.
Tuesday's earthquake, which was followed by several aftershocks, struck as Nepalis were coming to terms with the devastation from last month's 7.8 quake, which packed a punch more than five times greater and was centred west of Kathmandu.
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