Firefighters joined their colleagues from the police at HMP Ranby where a disturbance involving prisoners is ongoing.
Shortly after 7.30pm around 15 firefighters arrived outside the prison and began putting on their full kit before walking in through the main gate.
Officers carrying shields and other equipment were also seen going into the prison earlier.
More top news
The Independent has announced it is to cease publication and go online only from the end of March.
Bruce Carr QC, who led the government's industrial relations review, tells ITV News the Trade Union Bill will give employers too much power
A family pet was repeatedly kicked to within an inch of its life by burglars who broke into a home, police have said.