The long-running drama has aired five episodes a week, Monday through Friday, since 1992.
"The TV environment is changing fast and we're moving with our viewers," TVNZ chief executive Jodi O'Donnell said in a statement.
"For some time, we've been reimagining what is possible for Shortland Street."
The announcement comes after a significant restructure aimed to remedy the state-owned broadcaster's "difficult financial position," which resulted in 72 roles being axed. Funding for the long-running soap opera had been under question.
O'Donnell said the decision was influenced by TVNZ's digital-first strategy.
"We have an extremely engaged online audience for Shortland Street and we want to take the show successfully into the future and ensure its ongoing relevance," she said.
South Pacific Pictures chief executive Kelly Martin said the 34th season of Shortland Street would focus on quality over quantity.
"Fewer episodes mean a greater focus on creating the storylines that will cut through with audiences in a competitive market," he said.
"We'll bring all the things Shorty viewers love on steroids for three days per week, with stories that dig deep into real-life and topical issues in New Zealand."
