"I would like to express my heartfelt condolences. Please convey my sympathies to those directly affected, and to the relatives of the victims. I wish a swift recovery to all those injured," Angela Merkel wrote in her letter to Dmitry Medvedev, released by the German government's press service.
German Foreign Minister Frank-Walter Steinmeier also sent his condolences to his Russian counterpart, Sergei Lavrov.
The death toll from the accident at Russia's largest hydropower plant in south Siberia early on Monday has reached 10, with 14 people injured and dozens still missing
Two water ducts collapsed at 08:15 local time (00:15 GMT) at the Sayano-Shushenskaya, flooding a turbine hall. The disaster is believed to have been triggered by the explosion of an oil transformer while workers were carrying out repairs.
RusHydro, the owner of the Sayano-Shushenskaya station built in 1978, has said it is facing 1.5 billion rubles ($46 million) in monthly losses due to the accident.
The search efforts are set to continue through the night as more pumps and other equipment arrive at the scene.
The south Russian republic of Ingushetia was hit early in the morning by its worst attack for several years when a suicide bomber rammed a minivan full of explosives into the gates of the police headquarters in the city of Nazran, killing at least 20 people. Up to 138 people, including 10 children, have been reported as injured.
The explosion left a crater about 4 meters wide and 2 meters deep. The blast triggered more explosions as ammunition detonated in the police headquarters. The blast shattered windows and smashed balconies in residential buildings within a radius of 500 meters. Some 30 cars parked nearby were destroyed, Russian media reported.