The Dharahara Tower, built in 1832, was a landmark that had been open to visitors for the last 10 years and had a viewing balcony.
A stump just 10 metres (33 feet) high was all that was left of the 14-storey structure. Several bodies were brought away from the ruins.
At the main hospital in Kathmandu, people with broken limbs and arms were being rushed in for treatment. Crowds and volunteers formed human chains to clear the way for ambulances to bring in the injured.
Television news footage showed people being treated on the streets outside hospitals and several bodies lying in rows, covered in blankets.
Kathmandu is home to ancient, Hindu temples. Photographs posted online showed buildings reduced to rubble, with large cracks along roads and residents sitting in the street holding babies.
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