The epicentre of the quake was in Sonepat in Haryana, about 90 km from Delhi, and its aftershocks were also felt in northern states like Uttarakhand and Jammu and Kashmir.
"It is not 6.6 intensity, it is 4.2 on the Richter," an IMD official told.
The IMD website described the quake as "slight" and the timing as 23:28:18 hours.
Fire officials and Delhi Police said they had not received any report of damage or building collapse.
The temblor was particularly felt in east Delhi where thousands of people left their homes and came out on the streets.
"All the furniture in my house started shaking just as we finished dinner," said Vinod Kapoor, a resident of east Delhi.
In other parts of the capital too, people ran out of their homes in fright when their furniture started rattling alarmingly and cupboards and fans started swaying.
"A lot of panic here... my network is gone. People came out of their homes. Children started crying and everyone was on the roads," said an IANS correspondent who lives in a women's hostel in south Delhi.
Throughout the city, people called up relatives and friends, and asked after their well-being.
"At first I heard a muffled sound - like a subdued explosion in a tin - and then felt the quake for about 10 seconds," said Gurgaon resident Gulshan Luthra.
The quake had residents in Faridabad running out of their homes too.