Police special forces in Cologne descended on a job centre today after witnesses reported seeing an armed woman inside.

Officers were already at the building to detain a man allegedly threatening employees, who had also been accused of making death threats at a nearby refugee asylum centre.

But police were then approached by a terrified employee who reported seeing an armed woman on the loose in the building, sparking mass panic.

Employees were told to lock themselves in their offices and to stay inside while police searched the building in Sulz, in the west of Cologne, for the woman.

Police special forces in Cologne have descended on an employment agency building today after witnesses saw an armed woman inside

Alert: Police have descended on a employment agency centre in Cologne this afternoon

There are reports that as many as five people may have been arrested. It is not yet known if the alleged armed person was one of them.

Police said in a tweet: 'Police operation at job centre in Luxemburger Street due to threatening behaviour. Information over bomb threat is false.'

According to the local Express website, the incident unfolded after staff felt threatened by a group of jobseekers from Muelheim, to the north of Cologne, and called police.

Police arrived at the building around 3pm to arrest the man, who had allegedly been involved in a fight at a refugee centre in which he had threatened to kill another man.

Local media reported that police said the situation was 'unclear' but that the building was being searched.

Of the five people arrested, four were later set free and one remains in custody, according to Express.

People are gradually being allowed out of the building this afternoon and immediately started calling their relatives, local news websites report.

Police confirmed on Twitter that the search of the building has ended, and that nothing suspicious was discovered.

The incident comes with Germany on high alert after the country was rocked by four bloody attacks in a week.

A suspect had just been detained on a different matter at the building in Germany's fourth largest city when witnesses said they saw the armed woman walking around in the building

The deadliest attack came last Friday when a German-Iranian teenager who was born and raised in Munich opened fire at a shopping mall, killing nine people before turning the gun on himself.

He had been under psychiatric treatment and investigators say he was obsessed with mass shootings, including Norwegian rightwing fanatic Anders Behring Breivik's 2011 massacre.

They have ruled out an Islamist motive, saying the assailant had far-right 'sympathies'.

On July 18, an asylum seeker from Afghanistan or Pakistan slashed train passengers and a passer-by with an axe and a knife in Wuerzburg before being shot by police.

And on Sunday, a failed Syrian asylum seeker blew himself up outside a music festival in Ansbach, wounding 15 people at a nearby cafe after being turned away from the packed open-air venue. IS claimed both attacks.