A series of earthquakes jolted Russia's Pacific island of Sakhalin on Saturday, sending terrified residents into the streets, Russian media said.
There were no immediate reports of damage or injuries.
Interfax news agency said the tremors, each one stronger than the last, began shortly after 11 p.m. on the island north of Japan.
It said the quakes had caused walls of homes to shake in Yuzhno-Sakhalinsk, the island's largest town about 40 km (25 miles) south of the epicentre.
Local journalists told Russian television there had been 12 shocks in the space of nearly two hours.
They said residents had poured out of houses clutching a few possessions and were intending to spend most of the night outside. Some had left for summer homes in the countryside.
Mr Mikhail Baryshev of Russia's Emergencies Ministry told RTR state television there had been more than 20 shocks, but said all had registered five or less on the Richter scale. Two ministerial groups were investigating possible damage or injuries.
Interfax said power supplies flickered on and off and telephone links were shaky, making it difficult to determine what damage had been caused in outlying areas of the island.
It said the first tremor, with its epicentre near the village of Sinegorsk, was registered at 3.8 with subsequent tremors at 4.8 and 5.2. Each shock was registered slightly further to the south.
The agency said heightened seismic activity had been noted in recent weeks.
An earthquake on Sakhalin in 1995 measured at 7.5 left more than 2,000 people dead. Other earthquakes in former Soviet republics have had much higher death tolls, including a tremor in Armenia in 1988 which killed some 25,000 people.