The quake struck around 5:37 am local time (0037 GMT) at a depth of about 20.5 kilometres (12.7 miles), the US Geological Survey said.
The USGS estimated that "little or no population" would be exposed to landslides from the quake, and the Tajik emergency committee later said that no victims or damage were reported.
The quake's epicentre appeared to be in Gorno-Badakhshan, a semi-autonomous eastern region that borders Afghanistan and China, about 67 kilometres from the small mountain town of Murghob.
A 5.0-magnitude aftershock hit the area about 20 minutes after the initial quake, followed by a 4.6-magnitude quake.
The sparsely populated territory is surrounded by the towering Pamir Mountains, some reaching 7,000 metres (22,965 feet) above sea level, and is home to Lake Sarez.
The aquamarine-coloured body of water -- formed as a result of an earthquake in 1911 -- is among Tajikistan's largest lakes.
Located behind Lake Sarez is a natural dam deep in the Pamir Mountains, and experts have warned of catastrophic consequences if the dam were breached.
With a population of 9.5 million people, Tajikistan is the most impoverished former Soviet republic, and like much of the rest of Central Asia is highly prone to natural disasters, with a long history of floods, earthquakes, landslides, avalanches and heavy snowfalls.
Earlier this month, nine people died in a February 15 avalanche in Gorno-Badakhshan, while another person was killed the same day in an avalanche on a highway near the capital Dushanbe.
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