Armed police stormed a busy office building - only to realise they had gone to the wrong address.
Firearms officers from Cambridgeshire Police were called to reports of an armed robbery on Tuesday afternoon.
They were told the incident was happening at a branch of Premier Travel so rushed to the firm's headquarters in Cambridge.
It was only when about five patrol cars and an armed response unit arrived and officers burst into the building that they realised they should have been about 15 miles away in Newmarket, Suffolk.
A Cambridgeshire police spokesman said: "We received reports of an armed robbery at about 1.40pm yesterday afternoon in Milton Road, Cambridge.
"Armed officers were deployed, however, upon arrival it was established the incident location was in Newmarket, Suffolk.
"It is unfortunate that members of the public were alarmed by this, however we were responding to calls for service which was reported from a location in Cambridge."
Onlookers said they feared they were caught up in a Paris-style terrorist incident.
Shop owner Mary Anton told the Cambridge News: "It was so scary seeing the armed police especially with what has been happening in Paris. It is quite tense everywhere at the moment."
Suffolk Police arrived at the correct branch of the travel agent where they Tasered and arrested a man after reports that staff had been threatened with a knife.