A police community support officer patrolling the town centre tried to chase armed robbers who smashed their way into a jewellers with an axe this morning.
The PCSO was walking past Ernest Jones in Clarence Street as thieves struck in broad daylight at 10.38am in front of frightened shoppers.
One of the men driving what was described as an off-road type motorcycle, was riding in circles, and "going berserk", terrifying passers by.
The thieves escaped towards John Lewis, driving toward Kingston bridge.
JD Sports worker Adrian Kenyon, 24, heard screaming from outside and a group of woman ran into the shop saying they have got axes.
He said: "There was a guy on a motorbike going round in a circle going nuts. They were pretty brave. They were out there for five to 10 minutes.
"There were people running around. Some were standing looking. They were petrified."
Another onlooker said: "There was a PCSO outside. He tried to chase them but he didn't have much luck."
Police are still interviewing shop staff at the jewellers.
They have not yet said what has been stolen or the value of the robbery.
There was no sign of damage to the outside of the shop as the robbers used the axe to smash through to the glass cabinet.
PCSOs have faced criticism since their introduction amid confusion about their roles leading to them being dubbed "plastic policemen".
They cannot arrest people but can issue fixed penalty notices for littering or cycling on the footpath.
But senior officers believe they play a vital role in community relations and take on low level responsibilities, freeing up police officers to fight crime.