Two detectives arrived at the Herald offices in central Auckland at about 3:30pm.
Both refused to comment on what they were seeking, but a Herald on Sunday lawyer confirmed police had executed a search warrant.
The paper had complied with their requests, he said.
TVNZ has also reported that a search warrant has been executed at its Auckland headquarters.
DVD copies of field footage of the meeting between National Party leader John Key and Act's Epsom candidate John Banks at a Newmarket cafe earlier this month were handed to police this afternoon.
Police spokesman Grant Ogilvie said no further details could be provided about the inquiry at this stage.
"The police investigation is continuing and search warrants will be issued this afternoon and tomorrow and we'll be speaking to a number of people with information connected to the investigation.''
Earlier this afternoon, Justice Helen Winkelmann refused to rule on whether the "teapot tapes'', recorded by freelance cameraman Bradley Ambrose and given to the Herald on Sunday and TV3, were illegal.
She said granting a court declaration would prejudice the ongoing police investigation into the tapes, which feature the conversation between Mr Key and Mr Banks.
Justice Winkelmann said the facts of the case were still contested.
"I have not reached any view on whether this was a private communication,'' Justice Winkelmann said in her decision.
"Indeed my decision turns upon the inadequacy of the evidentiary material before me to reach such a view, and in any event, the inappropriateness of my undertaking a mini trial as to whether certain conduct constituted a criminal offence ... in advance of a police investigation or trial.''
Ambrose was seeking a declaration in the Auckland High Court on whether the conversation was private.
It is at the court's discretion to grant a declaration.
The main issue was not whether the conversation was private, but whether such a declaration would interfere with the police investigation, which began after Mr Key laid a complaint.
Today's decision means legal doubt remains over whether the conversation was private, and it may be illegal to publish the tape.
Up until now media with copies of the tape or a transcript have been reluctant to publish because of the risk of legal action.
Police had wanted to conduct the searches of a number of media organisations on Monday, but decided to wait until after the court's decision was released.
Mediaworks' spokeswoman Rachel Lorimer said they were not expecting to receive a search warrant until "tomorrow at the earliest''.
Yesterday Solicitor-General David Collins, QC, appearing for the Crown, told the court a declaration would be outside the court's jurisdiction because it was proper for police to conduct its affairs independently and objectively.
But Ambrose's lawyer Davey Salmon replied that the declaration would not be binding, nor would it prevent the police from bringing a case to be tested in a criminal court.
He and TV3 lawyer Julian Miles, QC, agreed that the conversation was public, conducted in the middle of a "political theatre'' to which media were invited.
Mr Miles also argued that the content of the tape was in the public interest.
"There is a duty on the media in these circumstances to bring significant information to the electors.''
Mr Salmon said no one at the event was asked not to listen to the conversation or not to record it - despite the request to remove recording devices away from the table.
The court viewed raw camera footage showing a print journalist in the cafe doorway close enough to listen and to record.
Mr Collins replied that the assertions from Ambrose, who claims he recorded the conversation accidentally, were contested.
He said two people were entitled to a private conversation regardless of whether it took place within the context of a political event.
