Residents were alarmed by a loud boom and billowing 'smoke' after a reactor unit tripped at Heysham 2 power station.
The loud noise and plume of steam came from the power station site on Wednesday at around 5pm.
EDF, owners of Heysham 1 and 2, said there was "no reason for concern".
Three fire trucks were sent to the site after a call from a member of the public, but no action was needed.
"This evening one of the units at Heysham 2 power station came offline," said an EDF spokesperson.
"This was not planned and noise caused by steam venting may have been heard by local residents.
“This steam venting is normal when a reactor comes offline and is no reason for concern. Work is under way to establish the cause of the trip and bring the unit back online.”


Lancaster-Morecambe train services cancelled amid heavy rain warnings
Pair jailed for violent attack on man in Lancaster street
Panjab Warriors interview: "Morecambe FC will never be in danger while we are owners."
Canal charity gets the ‘hump’ as Lancaster Canal bridges suffer more collision damage
Lancaster wills company donates thousands to help local community groups making a difference
Morecambe Bay Curriculum wins top award
Lancaster film director's latest action movie now showing in UK cinemas
Appeal after Jack Russell dog found collapsed in Lancaster
Lancaster food companies announced as finalists in new Taste Lancashire Producer Awards
New student apartments block opens in Lancaster
Former BBC reporter and ex-Heysham shipping chief launch popular maritime podcast
Lancaster children get life-saving advice at 'Crucial Crew' water safety event
Crews tackle house fire in Heysham
Police appeal after 20 motorbike thefts in 30 days in Lancaster and Morecambe area
Truck driver jailed for causing death of six-year-old Lancaster girl
Former Morecambe Football Club co-chairmen break silence after shock resignation from board
Royal Lancaster Infirmary ward closed to visitors due to norovirus outbreak
Morecambe Football Club stalwarts resign from board
Heysham coffee shop couple take over Morecambe craft ale bar
Morecambe seafront cafe reopens

