A deadly magnitude 7.3 earthquake has struck Nepal and sent aftershocks through neighbouring India, two weeks after a devastating quake killed more than 8,000 people in the Himalayan nation.

At least 45 people are known to have been killed and 1,115 people injured in Tuesday's quake, which struck the town of Namche Bazaar near the Mount Everest base camp, Nepalese officials said.

Earlier on Tuesday, in Kathmandu, police issued a public warning calling for people to stay in open areas and to send text messages instead of making calls, to prevent the network from becoming jammed.

Al Jazeera's Andrew Simmons, reporting from Kathmandu, said the quake was so powerful that it made the building he was in "feel like jelly".

NOTES FROM KATHMANDU I was at the Dirghayu Guru Hospital and Research Centre in Mitrapark in Chabahil area of eastern Kathmandu. There were about 20 patients lying on beds in the car park - mostly earthquake victims from the April 25 earthquake. Head nurse Shrijana Shrestha, 37, in the intensive care unit, said that when Tuesday's quake struck, patients were shouting and terrified and tried to get out of their beds. When I was in Naya Bazaar, there were some buildings with cracks and people were walking around them. People are pitching tents because they were terrified that there would be another earthquake. They were scared of the building coming down while they were inside. I went to an open ground in Chabahil and people were pitching temporary shelters with tarpaulins, bamboo and bricks. The second earthquake was strong and really shook people up. - Al Jazeera's Annette Ekin in Kathmandu

India's home ministry said another 17 people were killed in India, mostly in the northern Bihar state, and tremors were felt as far away as New Delhi.

One person was killed in Tibet, Chinese media said.

The quake was measured at a shallow depth of about 18km, the US Geological Survey reported. A series of aftershocks, including one 6.3 magnitude tremor, later hit in the same Namche Bazaar area.

At least 19 buildings collapsed across the country, Nepalese officials said, including 10 in Kathmandu.

A 7.8-magnitude earthquake struck Nepal on April 25, killing at least 8,046 people and injuring more than 17,800.

As rescue efforts unfolded, the Nepalese army confirmed that a US helicopter on a rescue mission to Charikot with eight people aboard had gone missing on Tuesday. It was last spotted at 4:45pm local time at Tamakoshi, north of Kathmandu.

Nepalese army Colonel Bishwas Bikram Shah said a ground and rescue mission was to be launched at first light.

He said there was a powerful aftershock 45 minutes after the main quake was felt.

A woman who works for a finance company in Thamel, in Kathmandu, told Al Jazeera that she had clung to a pillar inside her building when the quake struck.

"I was screaming. It felt like the house was falling," she said.

There was "utter panic" in Kathmandu following the quake, Al Jazeera's Annette Ekin reported from the city.

"The earth just started rolling. Everyone ran out onto the streets and all of the shops are now shuttered," she said.

She said the quake seemed to last about 30 seconds.

Hours after the quake struck, no one in Kathmandu appeared willing to go back indoors, Al Jazeera's Ekin said.

"Everyone is outside in the streets. At my hotel, all of the staff and guests are sitting around outside, waiting for more information," she said.

She later went to Kathmandu's Nayabazar district, where a four-storey building had collapsed.

While there were unconfirmed reports of people trapped under the rubble, she said authorities outside the building said no one had died.

Quick response

Al Jazeera's Subina Shrestha, also reporting from Kathmandu, said emergency services were quick to respond to the new quake.

"The army, the police, all managed to come out almost immediately," she said.

"At the hospital, because there were already volunteers working there. They managed to provide services quickly."

Al Jazeera's Shrestha said it was difficult to estimate the extent of the damage, because although this earthquake was smaller than the one two weeks ago, the damage was more spread out and it would take emergency services time to reach affected areas.

"It's just the beginning," she said.

"There have been landslides, there are buildings where they haven't been able to remove the debris. So it will take some time."