KATHMANDU, Nepal — Many survivors of Nepal’s most recent earthquake remain cut off by blocked roads in isolated villages, a U.N. official said Wednesday, after this Himalayan nation suffered through its second major quake in less than three weeks.

The magnitude-7.3 earthquake shook the impoverished country Tuesday, killing at least 79 people and injuring more than 2,300, just as it was beginning to rebuild from a devastating April 25 earthquake.

The most recent quake hit hardest in deeply rural parts of the Himalayan foothills, hammering many villages reached only by hiking trails and causing road-blocking landslides.

“Damaged houses were further damaged or destroyed. Houses and schools building spared before were affected yesterday, roads were damaged,” said Jamie McGoldrick, a top U.N. official in Nepal.

Among 14 quake-hit districts, some are barely accessible, and a large part of the affected population could not be reached easily because of damaged roads.

“Some are even difficult to reach by helicopter. We are facing monumental challenges here to support the government in these districts to have a credible response,” McGoldrick said.

On Wednesday, officials with bullhorns walked through the worst-damaged streets of Chautara, a small town northeast of Kathmandu, calling for people to leave buildings in danger of collapsing after Tuesday’s quake.

Most people, though, had fled into the open the day before and had spent the night in tents or under plastic tarps.

Chautara, a foothills town, became a hub for rescuers and humanitarian aid after the first earthquake. Officials there said at least three people had died and more than 60 were injured in the new quake.

Meanwhile, American and Nepali aerial reconnaissance teams expanded sweeps over earthquake-damaged regions Wednesday in the search for a U.S. Marine helicopter that lost contact during an aid mission after the latest deadly temblor in the Himalayas.

Six U.S. Marines and two Nepali soldiers were aboard the chopper that was reported missing Tuesday just hours after a 7.3-magnitude quake that killed at least 76 people in Nepal.

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