No casualties or serious damage were immediately reported from the temblor, which hit at about 1:35 a.m. local time in an area some 22 miles away from the Uzbek city of Ferghana, which has a population of more than 200,000.
In Andijan, the next largest city in Uzbekistan's Ferghana Valley, roughly 60 miles from the epicenter, residents told The Associated Press that many people had left their homes in panic and were standing in the streets.
A duty officer at the Emergency Services Ministry in the Kyrgyz capital, Bishkek, said he had no precise information about the fallout of the quake.
A Russian news agency reported people feeling the quake as far away as Dushanbe, the capital of neighboring Tajikistan, at least 185 miles southwest of the epicenter.
Online news portal Kloop.kg cited the mayor of one of the villages in Kyrgyzstan closest to the quake, Kyzyl-Kiya, as saying that the plaster had been shaken off the walls of some old homes, but that there were no significant indications of damage.
"I am with the people and trying to keep them calm. Police, emergency services, power and water utilities, everything is working," Mayor Khabiybulla Kalmurzayev told the site.
According to unverified online testimonies on the European-Mediterranean Seismological Centre, the temblor also was felt to the north in the town of Talas in Kazakhstan, 125 miles from the epicenter.
"My parents ran into my room and got me and my 9-month-old son up. The floor was shaking and the furniture was trembling. We all rushed to the entrance door and stood under the door frame for 5 minutes, being afraid of aftershocks," a resident in Talas wrote.
Quakes are a relatively frequent occurrence in this mountainous region of former Soviet Central Asia.
A 6.6-magnitude quake near Kyrgyzstan's borders with Tajikistan and China flattened a remote mountain village in July 2008, killing at least 74 people.
A series of small shakes, the strongest registering 5.4 on the Richter scale, also struck earlier this year about 40 miles from the commercial capital of Kazakhstan, Almaty.