Japan's Meteorological Agency registered the first earthquake with a preliminary magnitude of 6.4 off Sakhalin. It was felt in nearby Japan but there were no immediate reports of damage or injury there.
A Reuters reporter on Sakhalin said he felt three tremors, over a two-hour period. The third, at about 1030 IST was the most intense, said the reporter who was in Yuzhno-Sakhalinsk, the main city on Sakhalin island.
He said the second tremor made light fittings swing, while chairs moved across the room during the third.
Local office workers ran on to the street fearing the third tremor was a major quake they had been anticipating.
''Just about everybody in the building dashed to the street.
We've been hearing so much about earthquakes in the news recently and after knowing about the two quakes today, we thought that this was 'the one','' said Anastasia Lekhnova of Troop Service, a security firm.
The emergencies ministry said a 30-year-old woman died when the building she was in collapsed in the town of Nevelsk. A man also died in the town as he was being evacuated from a building.
Two other people were hurt.
''Cracks appeared in buildings and furniture fell over inside apartments, but there is no damage to other towns, only to Nevelsk. Energy supplies have also been disrupted,'' said Sergei Viktorov, the local Russian emergencies ministry spokesman.
Russian President Vladimir Putin dispatched Emergencies Minister Sergei Shoigu to the quake-stricken area, charging him with the task of helping those who lost their homes and property in the disaster, Russian news agencies reported.
The local offices of international consortium Sakhalin Energy and Exxon Mobil Corp, which is developing massive oil and gas resources off Sakhalin, sent employees home.
In 1995, the island was hit by Russia's worst recorded earthquake, which killed 1,989 people from the town Neftegorsk.
Yuri Levin, acting director of the Yuzhno-Sakhalinsk seismic station, said there was no immediate reason to panic.
''Sakhalin is in a seismically sensitive zone and there is a chance of a major earthquake sometime in the next 50 years.'' A small tsunami caused by the earthquake, with waves of up to 30 cm hit the west coast of Japan's northernmost main island of Hokkaido without causing damage.
REUTERS PD RAI2016