Authorities said the two trains were traveling in opposite directions on the bridge linking s Denmark's islands. Aerial TV footage showed a front side of the passenger train ripped open. Photos showed crates of beer on the freight train and a tarpaulin on top torn in pieces.

Jesper Nielsen told Denmark's TV2 he was riding on the passenger train and it "was out on the bridge when there was a huge 'bang' ... very quickly thereafter, the train braked."

The rail operator, Danish Railways, told Denmark's TV2 the victims were passengers on a train going from the city of Odense, on the central Danish island of Funen, to the capital of Copenhagen when the accident took place about 8 a.m.

Police declined to comment directly on a report from Denmark's TV2 channel that a large freight container had likely fallen off the cargo train.

"It is much too early to speculate as to what might have caused it," chief police investigator Joergen Andersen told reporters. "It has been a pretty serious accident."

The accident, in which 16 people were injured, took place on a road-and-rail bridge, part of the Storebaelt system of bridges and a tunnel that link the Danish islands of Zealand and Funen. The system was closed to cars overnight because of strong winds but trains were allowed to continue using it.

Police spokesman Lars Braemhoej said one possible cause of the "considerable damage" on the passenger train was getting struck by cargo from the freight train, but noted that authorities "do not know precisely what caused the accident."

Kasper Elbjoern, spokesman for the Danish brewery group Carlsberg, confirmed that a freight train transporting its cargo was involved in the accident.

Police urged passengers to contact relatives and tell them if they were safe and urged people not to share photos or videos of the accident.

Flemming Jensen, the CEO of state-owned Danish Railways, said police and the Danish Accident Investigation Board were investigating. He said the operator "will contribute everything that we can to the investigation."

Bo Haaning of the Danish Accident Investigation Board was quoted as saying it could take months before the cause of the accident could be determined.

The government agency responsible for Danish railways said on Twitter that no further trains would cross the Storebaelt link on Wednesday, adding it was aiming to allow train crossings to resume Thursday. Road traffic resumed Wednesday with a 50 kph (31 mph) speed limit.

"Ordinary Danes on their way to work or heading home from the Christmas holidays have had their lives smashed," Prime Minister Lars Loekke Rasmussen said as he issued his condolences.

Denmark's Queen Margrethe said the "terrible accident ... touches me deeply."

In 1988, eight people were killed and 72 injured when a train derailed because of high speed near Soroe, west of Copenhagen.

Denmark's worst train accident occurred in 1919, when an express train collided with a stopped train in Copenhagen due to a dispatcher error. A total of 40 people were killed and some 60 were injured.