According to US Geological Survey, the quake struck off about 15km south-west of the capital at 03:23 am and was followed by three aftershocks of 5.9, 5.5 and 5.1 magnitude.
US officials reported bodies in the streets and an aid official described "total disaster and chaos."
A spokeswoman for Catholic Relief Service aid group, Sara Fajardo said, "There must be thousands of people dead."
The country is said to be home to over 200 Indians, most of whom are policemen deputed as part of the United Nations Stabilisation Mission in Haiti (MINUSTAH).
"We have not been able to contact with the Honorary Indian Consul General in Haiti, Marie Andrine," Deputy Indian Ambassador of Cuba was quoted by news agency as saying.
Buildings, including the presidential palace and a hospital, are said to have collapsed, and rescue efforts are under way.
US President Barack Obama has offered immediate help and asked his officials to gear up for sending relief material to Haiti as soon as possible.