Romania's National Institute for Earth Physics put the quake at magnitude 5.2, while the US Geological Survey gave it a magnitude of 5.6.
"The epicentre was in the seismic region of Vrancea at a depth of 100 kilometres (60 miles)," the institute's spokesman Mircea Radulian told AFP after the quake hit around 1:20 AM (local time).
The Vrancea region, northeast of Bucharest, has experienced some of Romania's most deadly tremors, notably in 1977 when a 7.2-magnitude quake killed more than 1,500 people.
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