The small market town of Thornbury, in South Gloucestershire, is at the centre of a major security operation ahead of the Nato summit which begins in 48 hours time.
Around 2,000 police officers from forces across the country will be using headquarters in the town every day during the international security meetings.
They have taken over the former South Gloucestershire council buildings in Castle Street.
Police have travelled to Thornbury from Kent, Northumbria and Scotland to join colleagues from the Avon and Somerset Constabulary in readiness for the two day summit at Celtic Manor near Newport which starts on Thursday.
A fleet of police riot vans have been sent to Thornbury and have been seen driving into the police headquarters with documents named "Operation Ismay".
Officers have been deployed to keep watch on roads and bridges along the M4 leading to Celtic Manor.
Leaders of 28 Nato member states and 30 countries that are partners will be attending the summit which is the first of its kind to be held in Britain for 30 years.
They include US President Barack Obama, German Chancellor Angela Merkel, and President Francois Hollande of France.
Some of the delegates will be arriving at Bristol Airport in the next 24 hours.
Nine thousand officers from across the country are taking part in the security operation with many expected to be briefed in Thornbury.
A police spokesman confirmed that Thornbury was to be a centre for operations.
He said: "During the Nato summit, the former council offices on Castle Street will be used as a base for briefing officers involved in the policing operation.
"At a peak, up to 2,000 officers from across the country will be briefed there each day before being deployed both within Avon and Somerset and in other areas."
Sniffer dogs have also been spotted at Bristol airport to check the terminal building was safe before high-profile politicians fly in this week.
Police were seen checking public areas and patrolling car parks, allowing trained dogs to search bushes and pathways.
Some of the 2,000 delegates who will be attending the summit will be staying at hotels in Bristol and Bath. A Government spokesman said virtually every hotel along the M4 corridor between Newport and Swindon will be full.
Thornbury Castle was rumoured to be in line for a high-profile guest.
The hotel at first declined to comment on whether the hotel was being used by attendees of the summit "for security reason".
But a spokeswoman for Luxury Family Hotels, which runs the hotel, said she was "not aware of any customers staying for the summit".
There is nothing hidden about the operation in Thornbury, with blue signs directing police from across the country into the former council buildings on Castle Street.
But questions still remained from residents about the reason why coach-loads of officers are pitching up in their town.
At T & J Owen florists on the High Street, Sarah Gibson, 24, said: "Nobody has said anything. We have only heard rumours from customers.
"There have been riot vans and police cars coming up and down the road since the weekend but we only assume it is to do with the Nato summit.
"Whether people are staying at Thornbury Castle, we're not sure. Stars do stay at the castle."
In the PDSA charity shop on the High Street, a member of staff, who asked not to be named, said: "It is the Barack Obama meeting, that's what we have heard."
Another member of staff added: "I heard in Zumba yesterday. Someone told me it was because of this convention but we don't know any more than that."
John Riddiford, of Riddiford convenience store, also on the High Street, said some people had hardly noticed the police presence building.
He said: "For some people it's just completely passed them by. It's just gone over their heads."