A sinister caller warned that 'Cologne's main station will soon be in the air' in a bomb threat that forced police to close the transport hub amid heightened tensions following yesterday's Berlin attack.

The entire station was closed after the call at 6.28pm, one of the busiest periods for commuters at a time when thousands are also shopping in the nearby city centre ahead of Christmas.

Police evacuated the entire building, which is the city's main transport hub, prompting major rail delays likely to affect thousands of people who use the station every day.

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Cologne's main train station was briefly evacuated after a telephone bomb threat today, leaving hundreds stranded outside (pictured)

Police were seen surrounding the station amid hundreds waiting outside when it was closed after a caller warned 'soon Cologne's main station will be up in the air'

Both state and federal police rushed to empty the station after the caller told a call handler: 'Cologne's main station will soon be in the air!,' reports German newspaper Bild.

Hundreds were seen waiting outside after being herded out by police officers, who surrounded the building as sniffer dogs went to work trying to hunt out explosives inside.

But police have since announced that the threat was a false alarm, re-opening the station and allowing hundreds of people who were waiting outside back in.

The threat came as Germany remains on high terror alert after the brutal truck attack on a Christmas market in Berlin last night that left 12 people dead and around 50 injured.

The call came in hours after authorities announced they would increase the police presence and clear jail cells for New Year's Eve after last year's sex attacks.

In total, 1,222 criminal complaints were investigated last year, more than 512 of them accusations of sexual assaults, crimes that were largely blamed on migrants.

Hundreds were seen waiting outside after being herded out by police officers, who surrounded the building as sniffer dogs went to work trying to hunt out explosives inside

But police have since announced that the threat was a false alarm, re-opening the station and allowing hundreds of people who were waiting outside back in

The shocking numbers fuelled political tensions in Germany last year, heightening opposition to Chancellor Angela Merkel's controversial open-door policy.

The Chancellor is now under fire again after 12 were killed and around 50 injured when a stolen truck careered through a busy market square in Berlin last night.

Some believe it was a terror attack after reports from local media that the driver responsible was a refugee from Pakistan or Afghanistan who entered Germany in February.

In Cologne, there will be 66 prison cells available and they will be able to accommodate up to 100 people at a time, police have said.