The emergency services are dealing with what they are describing as a "small fire" at Hartlepool Nuclear power station, owned by EDF Energy.
Cleveland Fire Brigade said more than 10 fire engines were sent to the scene of the plant near Seaton Carew. The blaze has now been extinguished.
In a statement, Cleveland Police said there have been no injuries as a result of the fire and have reassured residents that although smoke can still be seen and noise heard from the site, the fire is out.
"During incidents such as this there are several procedures that take place, including the venting of steam generators.
"This particular process causes noise, which residents of nearby areas such as Seaton Carew may hear."
Police say any smoke is currently heading in a direction that does not cause any implications for the public.
Officers and fire crews remain on the scene as a precaution.
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