A man arrested after a three-hour siege at a bank was carrying a bomb, police said today.
Military and armed police surrounded the Co-operative bank, in Market Street, Watford, after the suspect threatened staff, Hertfordshire Police said.
A police spokeswoman said: "An explosive device of some kind - as yet we don't know what this is - has been removed from this individual."
Police said they secured the "successful arrest" after the man refused to leave the bank.
"Investigations into the nature of this device will continue," the spokeswoman said. "The suspect has been arrested and will be taken to police custody for interview."
The force said it was supported by specialist firearms experts in the military in making the arrest.
The man was forced on to his knees outside the bank as he was arrested by armed police officers, a picture published by the Watford Observer shows.
The black-haired suspect was wearing a short-sleeved white shirt and black trousers as he was held.
Sources said the incident was not thought to be terrorist-related.
Police were called to the bank at 10.18am to reports of a man threatening to harm members of staff.
Specialist firearms teams and military bomb disposal experts attended the scene in the centre of the town.
Witnesses described police marksmen aiming their guns at the bank and reported rumours that the man had a bomb strapped to his body.
Pat Sullivan, who works at local damp-proofing firm M Mansell, said police closed the main roads around the bank and the ring road, causing traffic to back up.
She said: "I've forced my way through the barriers to get in.
"There's so many people out there - the police, police cars, fire engines, press and, I guess, bomb disposal teams.
"There's groups of people out there just standing and waiting, the community is just wondering what's happening really. You can't walk out there because it's all cordoned off.
"The traffic's nose-to-tail because the police have closed most of the roads."
Hertfordshire Police said in a statement: "Safety of members of the public was paramount and a cordon was put in place and people were evacuated from nearby premises.
"There will be police activity in the town centre for a while to come. Understandably this caused concern within the community and we would like to thank members of the public for their co-operation in this matter."
Shop workers told of the panic when the area was evacuated by police.
Jacqui Bryan, from Edgware, who was working at Barratt Homes just behind the bank, said: "The police told everyone to move. We were just told to get out of the building. I thought it was a fire."
Ryan Saunders, 22, who was heading to work at nearby BHS at the time, said: "There were lots of people panicking, and then I saw the bomb disposal van speed past me. Everyone was desperate to get away."
His friend Michael Robinson-Collier, also 22, said: "It all kicked off as I was coming into town. I just saw all of the police rushing to the bank."
Local councillor Rabi Martin said: "As a ward councillor, I was anxious there was no threat to residents or staff. This is the last thing we want for Watford. But the main thing is that there were no casualties.
"The police reacted so quickly and decisively in evacuating the area. Watford town centre has so many different entrances for them to seal off, so their efforts were commendable."
A Ministry of Defence spokeswoman said: "Defence explosive ordnance disposal team supported the police in the incident, in accordance with normal military assistance procedures."