MOSCOW, Aug 26 (Reuters) -

All 250 passengers aboard an Air China flight from London to

Beijing resumed their journey after an unscheduled landing in

Siberia, Russia's state aviation watchdog said on Tuesday.

Earlier, Russia's civil aviation authority, Rosaviatsia,

reported that the crew of an Air China Boeing 777-300 opted to

land at an alternate airfield in the Russian city of

Nizhnevartovsk.

The preliminary reason for the diversion was said to be a

malfunction in one of the aircraft's engines.

Passengers spent 13 hours in Nizhnevartovsk airport, where

they were provided with food and soft drinks. A replacement

aircraft departed the airport at 1622 GMT.