Eighteen people were killed in a helicopter crash in the Krasnoyarsk region in Siberia on Saturday, the aviation watchdog and emergency services said.
The passengers, workers heading to their shift at an oil-pumping station, and three crew members died when the Russian-made Mi-8 aircraft knocked into the cargo of an adjacent helicopter as both were completing takeoff, watchdog Rosaviatsia said.
The incident occurred in the Vankor Field area in eastern Siberia, the watchdog said, at around 2 a.m. Vankor is the region's largest oil field, operated by Russian oil company Rosneft.
"A Mi-8 helicopter which was carrying external suspended cargo and no passengers completed takeoff first. Second to take off was a Mi-8 helicopter carrying passengers," the watchdog said.
"After takeoff, according to early reports, the Mi-8 carrying passengers knocked into the external cargo of the other helicopter, for reasons unknown. As a result it fell, broke apart and caught fire," the watchdog said, adding weather conditions were normal.
A commission has been set up to investigate the crash.
The helicopters' black boxes have been recovered, appear undamaged and will be sent to Moscow as part of the investigation, the state-run TASS news agency said, citing law enforcement agencies.
The other helicopter landed safely after the incident. The two aircraft were owned by UTair-Helicopter Services, a unit of Russian airline UTair.
In Russia, the helicopter operator predominantly works with oil and gas companies, transporting people and cargo for clients including Gazprom, Shell and Rosneft. It also works around the world on United Nations contracts, according to the company's website.