A chartered jet carrying Russia's major league ice hockey team Lokomotiv has crashed on take-off near the central city of Yaroslavl, with 43 deaths.
Two people survived with serious injuries after the disaster, which saw the jet burst into flames shortly after leaving an airport near the city.
It appears many of the team were aboard, heading to Belarus for the season's first match.
Russian reports suggest the Yak-42 plane may have struck a radio mast.
Witnesses saw it burst into flames shortly after taking off from the Tunoshna airport, about 250km (160 miles) north-east of Moscow.
Some of the wreckage and bodies fell in the nearby River Tunoshna, a tributary of the Volga.
All 11 foreign citizens on board the plane were killed, including the team's Canadian coach, Brad McCrimmon, and Swedish goalie Stefan Liv.
Russian player Alexander Galimov survived the crash with 80% burns along with a member of the crew. Local media briefly reported the player had died of his injuries, but a doctor at the local hospital later said he was still alive after undergoing surgery.
The second survivor was identified as Alexander Sizov, member of the eight-strong crew.
The chairman of the board of directors of the Kontinental Hockey League (KHL), Vyacheslav Fetisov, described the air disaster as an "irreparable loss for world ice hockey".
Ice hockey is the team sport of choice for many Russian men, along with football.
Flames 'nine storeys high'
The team, which had been due to play Dinamo Minsk on Thursday, also includes players from Germany, the Czech Republic and Slovakia.
A local policeman told the BBC Russian service he had seen the plane come down.
He said the plane had barely taken off before it plunged to the ground, and he saw "flames as high as a nine-storey building".
Local resident Irina Prakhova saw the plane going down, then heard a loud bang and saw a plume of smoke, the Associated Press news agency reported.
"It was wobbling in flight, it was clear that something was wrong," she said. "I saw them pulling bodies to the shore, some still in their seats with seatbelts on."
Russian aviation officials were quoted as saying the Yak-42 jet had failed to gain height and hit a radio mast, breaking up and catching fire.
The plane was operated by the Yak-Service company, Russia's aviation authorities said.
They said the jet entered service in 1993 and had a certificate of airworthiness valid until 1 October 2011.
The reigning champions Ufa had already started their first game of the KHL season, but abandoned the match when the gravity of the crash became clear.
"In such a situation, after their friends and colleagues died, the players of both teams considered playing to be absolutely impossible," KHL president Alexander Medvedev said.
The 10,000-strong crowd in Ufa's stadium held a minute's silence for the victims of the crash.
Running a live event page on the disaster, Sovetsky Sport reported that "grown men had wept like children" when they heard about it at the match in Ufa.
A photo from the stadium showed players with their hockey helmets removed, their heads bowed.
Another photo showed what were said to be the crew of the jet - three men posing confidently on a sunny day near an airliner.
On Twitter, Russians exchanged messages about a "black day" for ice hockey.
'Support for team and fans'
Interviewed by Ria-Novosti news agency, Vyacheslav Fetisov said there was an urgent need to support to the team and its fans.
"We now need to take a very calculated step towards creating a team in Yaroslavl - perhaps a new draft or a re-draft."
More than 2,000 fans wearing replica jerseys gathered outside Lokomotiv's stadium in Yaroslavl in the evening, paying their respects and singing team songs.
Fans in Trencin in western Slovakia lit candles for Pavol Demitra, while Czechs paid similar respects in the Old Town Square in Prague to honour the three Czech players who died.
Russian Ice Hockey Federation president Vladislav Tretiak said: "We have suffered an irreparable loss. I still cannot believe what happened. Our hockey has lost great players and coaches. It's just a terrible tragedy for the sport."
Gary Bettman, the commissioner of the North American National Hockey League, where a number of those who died had long careers, said: "Though it occurred thousands of miles away from our home arenas, this tragedy represents a catastrophic loss to the hockey world - including the NHL family, which lost so many fathers, sons, teammates and friends."
Russian President Dmitry Medvedev was due to address a forum in Yaroslavl on Thursday, and his spokeswoman said he would alter alter his schedule to visit the crash site.
The Russian president has promised to overhaul the industry and take out of service ageing jets from the Soviet era.
The country has a poor aviation safety record. In July this year a passenger plane crashed in northern Russia and 44 people died.