There have been reports of large explosions in South Auckland on Tuesday night, ranging from Waiuku to Otara.
Residents took to social media to report the loud noises, and emergency services were initially baffled by the cause.
"We heard the two loud bangs and it shook our house and we're out in Clevedon," one woman wrote on Facebook.
Northern fire communications shift manager Jaron Philips told Newshub they had received a call from Otara from a resident whose windows had been rattled by a large explosion.
Police say the explosions were caused by a police training exercise within the grounds of the Otahuhu Power Station that included the use of explosive demolitions.
Last week they had sent out a notice warning of the training between 4pm and 7pm, which would include "the use of explosive demolitions that may be heard by members of the public residing in the general area".