Four people were killed in Sikkim and 33 others received injuries there. In Bihar, a seven-year-old girl was among two dead. One more died in West Bengal. Of the five killed in Nepal, three casualties were reported from Kathmandu itself.
Tremors were felt in Lucknow, Patna, Kolkata, New Delhi and the National Capital Region.
Three aftershocks, of magnitude 5.7, 5.1 and 4.6 were also felt in Sikkim, says the India Meteorological Department.
Many buildings in the state have developed cracks, including the Sikkim Manipal University building.
There is no electricity in Gangtok and Darjeeling. Telephone lines have also snapped in some parts of Sikkim; phone lines are congested in West Bengal.
Five Indian Air Force planes have also been pressed into action for relief operations. Small Army columns in Sikkim have also been mobilised post the earthquake.
Prime Minister Manmohan Singh has spoken to Sikkim's Chief Minister Pawan Chamling and offered help. The Prime Minister has directed the Cabinet Secretary to call an emergency meeting of the Disaster Management Authority.
The quake comes just days after an earthquake of 4.2 magnitude hit Haryana's Sonepat district, sending tremors in New Delhi.
