Lincolnshire Police have cordoned off an area of South End in Boston.
There are numerous reports of officers outside the Royal Mail sorting office and Boston Grammar School.
One man claims armed police and four police cars have been seen in the area, with one parked across the road.
A member of staff at the Nikita pub said police were in the vicinity.
She said that two police cars and a police van could be seen outside the sorting office.
Lincolnshire Police have been approached for a comment.
This is a breaking news incident and we’ll bring you live updates throughout the course of the event in our live blog below.