Hundreds of shoppers gathered to watch 38 firefighters tackle a blaze at TSB that engulfed the roof of the bank.
It was the second major fire in as many days for the fire service.
The previous day, firefighters risked being blown up at a burning workshop in Wyberton’s Slippery Gowt Lane.
Seven cylinders of gas at the site had to be quickly removed to avoid disaster.
Together, the fires caused damage totalling more than £100,000.