At least six people were killed when a 6.3-magnitude earthquake struck the lower Himalayan region early Wednesday, leading to tremors rippling across north India and parts of Nepal and jolting people out of their sleep in scores of cities and villages.

The National Centre for Seismology (NCS) said the epicentre of the 6.3-magnitude earthquake, which struck at 1.57 am, was in Nepal, about 90 km east-southeast of Pithoragarh. The region has been experiencing lower magnitude quakes for the last few days.

Mild aftershocks were also felt in the Uttarakhand-Nepal region at 3:15 am and 6:27 am. The NCS said the magnitude of the two tremors was 3.6 and 4.3 respectively.

The National Earthquake Monitoring Centre of Nepal said a 6.6-magnitude quake was recorded at 2.12 am. The epicentre was Doti district.

Two moderate earthquakes preceded the stronger tremor that jolted western Nepal, a 5.7-magnitude tremor at 9.07 pm on Tuesday and a 4.1-magnitude one shortly after at 9.56 pm. The epicentre was the same, it said.

Six people were killed in the earthquake, Nepal's Home Ministry spokesperson Phanindra Pokharel said.

Five people who sustained serious injuries were rushed to the district hospital in Doti, Pokharel told PTI over the phone. A police post and eight houses collapsed due to the earthquake.

Bhola Bhatta, the acting chief at the District Police Office in Nepal's Doti, said all the six victims were killed by the debris of the houses damaged during the earthquake.

The tremors were felt in Delhi and the surrounding areas of Ghaziabad and Gurugram and even in Lucknow, jolting people out of their sleep.

Many people shared their experiences on Twitter, posting videos of people rushing out of their houses and neighbours gathering in groups, huddled over their phones as they tried to find out what had happened and where the epicentre was. One video showed a chandelier shaking.

"I'm just 80 km away from the centre of this earthquake.... I tell you guys.... I was in deep sleep. My table started hitting the wall.... Almirah made sound.... and my bed shook.... It was for at least 50 to 70 seconds," posted Dinesh Sharma, who said he is based in Pilibhit in Uttar Pradesh near the border.

"The tremor was absolutely clear in Lucknow too," added Tanmay Singh.

Neha Yadav, another Twitter user, said she is staying in Delhi for four years and had never felt such tremors.

Advocate Rahul Agrahari, who lives in Faridabad near Delhi, was eloquent in his description.

"It was like floor was hilling dulling so much Bec I sleep on the floor, Mujhe to lga bhoot h then Google kiya to got to know. Ek hamare sector ke log Kumbhkaran ke aulad koi bahar hi nahi aya (sic)," he said, describing how he was shaken out of his sleep because of the quake and thought it was a ghost. It was only after he checked Google that he realised it was an earthquake.

"It's 2 am and people are having a stroll on the streets.... Reason - #Earthquake," said Aakash Biswas and shared a video of people moving on a street.

Among those who went on Twitter was Union minister Meenakshi Lekhi. "Didn't want to tweet but one can safely say it did feel like an earthquake!" she wrote on the microblogging website.

Delhi Chief Minister Arvind Kejriwal also took to social media and wrote: "I hope all of you are safe."

Congress leader Radhika Khera urged people to "stay alert and stay safe".

Radio jockey Raunac said, "It was scary...extremely scary."

The resident welfare associations in Delhi said there have been no reports of any kind of damage or casualties in their areas.

"We have not received any report of structural damage or injury from any RWA. However, there was a bit of panic as people could not figure out what was happening. We were scared. People came out of their homes for a few minutes. However, things calmed down after a while," Atul Goyal, the president of the United Residents Joint Action, said.

Kritima Bhapta (25), a resident of Amar Colony in south Delhi, shared her experience, saying it was "scary".

"I felt tremors for 10 seconds straight. It was scary. Doors and windows were shaking and I could not figure out what was happening. I got to know from social media that it was an earthquake," she said.

"Omg just had #earthquake... I feel that in Delhi, hope everything is fine in Nepal (sic)," Krish Andrew said in a tweet.

People ran out of their houses in panic in a number of Uttarakhand towns as the tremors were felt across the hill state, including in Pithoragarh, Bageshwar, Almora, Champawat, Udham Singh Nagar, Nainital, Rudraprayag, Chamoli, Tehri, Pauri, Haridwar, Uttarkashi and Dehradun districts.

Many of them sent messages on their mobile phones to their relatives, informing them about their safety and enquiring after them.

A report from Pithoragarh, quoting District Disaster Management Officer B S Mahar, said there was no information of any damage to life and property from any part of the district.

"I suddenly woke up and ran outside after I heard my window panes rattling and saw the fan swaying," said Prabha, a resident of Kashni village in Pithoragarh.

"A second jolt was also felt at 6.29 am. But it was milder in comparison," a shopkeeper named Pramod Dwivedi in the Munsiyari sub-division of Pithoragarh said.

However, there was no official confirmation of the second jolt.

The Himalayan region in Uttarakhand and adjoining Nepal has been experiencing earthquakes of lower magnitudes for the last couple of days.

The United States Geological Survey (USGS) said the epicentre of the earthquake was at a distance of 21 km from Dipayal in Nepal.

The region experienced at least two earthquakes of 4.9 magnitude and 3.5 magnitude late on Tuesday evening, the NCS data showed.

A 4.5-magnitude earthquake had struck Uttarakhand on Sunday, with the epicentre 17 km east-southeast of Uttarkashi.