Russia on Thursday scoured the Urals region for a plane that went missing from an airfield with 12 passengers believed to be on board, including a local police chief, after a drunken party.
The emergency situations ministry said it was sending out six planes to fly over a vast area of 12,000 square kilometres (4,600 square miles) on Thursday searching for the Soviet-era Antonov-2 plane, which vanished without trace on Monday.
The plane "took off without authorisation from the Serov aerodrome at around 10 p.m., with apparently 12 passengers on board and one pilot," a police spokesman in the regional capital of Yekaterinburg said.
No remains of the plane have been found but the passengers are not answering their cell phones after an apparently spontaneous decision to take the privately-owned plane, which had been rented to monitor forest fires, for a trip.
The passengers included the traffic police chief of the town of Serov, as well as two women in their 20s and 30s, said Yekaterinburg police spokesman, Valery Gorelykh.
"We have evidence that the people on board were in a drunken state," he said.
Komsomolskaya Pravda tabloid reported that the passengers boarded the plane after a party for the Russia Day national holiday, leaving empty bottles on the airfield.
The head of the regional emergency situations ministry, Andrei Zalensky, told the daily that the party was believed to have set off to view waterfalls around 100 kilometres away.
The Antonov-2 single-engined biplane was produced in the Soviet Union from 1947, and is still used as a workhorse in remote areas of Russia.