By Ross Adkin and Gopal Sharma
KATHMANDU, May 12 (Reuters) - A fresh 7.3-magnitude earthquake struck Nepal on Tuesday, killing more than two dozen people in the Himalayan country and neighbouring states, as many buildings already weakened by a much bigger quake last month were brought down.
The earthquake was centred 68 kilometres (42 miles) west of the town of Namche Bazaar, close to Mount Everest and the border with Tibet, the U.S. Geological Survey said. It could be felt as far away as northern India and Bangladesh.
Buildings swayed in New Delhi, sending office workers scurrying on to the streets. Residents in the Indian town of Siliguri, near the border with Nepal, said chunks of concrete fell off one or two buildings.
Nepal's home ministry said the death toll from the quake had reached 19, with 981 injured.
Five people were killed in Indian states bordering Nepal - one in Uttar Pradesh and four in Bihar, officials said, and Chinese media reported one person died in Tibet after rocks fell on a car.
Nepal is still picking up the pieces from the devastation caused by last month's 7.8-magnitude earthquake, the country's worst in more than 80 years, which killed at least 8,046 people and injured more than 17,800.
Hundreds of thousands of buildings, including many ancient sites, were destroyed and many more damaged.
Mountaineers seeking to scale the world's tallest peak have called off this year's Everest season after 18 people died when last month's quake triggered avalanches on the mountain.
Dambar Parajuli, president of Expedition Operators' Association of Nepal, said there were no climbers or Nepali sherpa guides at the Base Camp.
"All of them have already left," Parajuli said.
In Lukla, the departure point for treks to Everest, buildings cracked and small landslides were triggered when the ground shook.
Locals said three teenage school students were injured.
Susana Perez from Madrid was on a 10-day trek with her husband to Island Peak in the Everest region and was about to reach Lukla.
"We saw the mountain in front of us fall down - earth and rocks. There were some houses underneath but it was not clear if they were hit," Perez said.
In Kathmandu, people panicked and rushed outdoors when the tremors began around 12.30, Reuters witnesses said. The quake was followed by at least half a dozen aftershocks, including one as big as 6.3.
Parents could be seen clutching children tightly, and hundreds of people were frantically trying to call relatives on their mobile phones.
Shopkeepers closed their shops and the streets were jammed with people rushing to check on their families.
"I'm heading straight home," said Bishal Rai, a man in his 20s, who said he was trying to contact his family in the north of the capital.
Medics and volunteers formed a human chain at a Kathmandu hospital to keep a path open for ambulances.
A volunteer at the hospital said five or six injured people had been brought in, two on stretchers. So far, few ambulances had arrived, he said.
Some aid and rescue teams, which were on their way back from Nepal, were considering whether to return to help.
"There is a huge concern for the people who may be living in structures that did not prove earthquake sound," said De Wojtek Wilk, CEO of the Polish Center for International Aid.
Wilk said his last team of medics were currently on their way back from Nepal, but he was wondering whether to send them back on a return flight.
Indian Air Force spokesman Simranpal Singh Birdi said one MiG 17 aircraft stationed in Kathmandu has been sent to Namche Bazaar to assess the damage.
At least four people were killed in Chautara town in Sindhupalchowk district, north of the Nepali capital Kathmandu, a spokesman for the International Organization for Migration said.
The new temblor also triggered at least three big landslides in the district, which suffered the heaviest death toll in last month's quake.
A district official there said 12 people had been injured.
"The latest earthquake has left us shaken. I am still trembling," said the official, Diwakar Koirala, when reached soon after the quake.
Rhita Doma Sherpa, a nurse with the Mountain Medicine Center in Namche Bazaar, near the epicentre, said the quake caused cracks in several buildings, including a school, but she had not seen major damage.
"It was lunchtime. All the kids were outside. Thank god," she said. (Additional reporting by Krista Mahr, Rupam Jain Nair, Doug Busvine, Sanjeev Miglani, Andrew MacAskill and Frank Jack Daniel; Writing by Paritosh Bansal; Editing by Raju Gopalakrishnan and Will Waterman)