The electorate will have a by-election following the general election, due to the death. The Electoral Commission has encouraged voters to continue to vote as their party votes will still be counted.
In a statement on Monday afternoon, the Act Party said it was in mourning for Christensen, who was also New Zealand's only registered specialist poultry veterinarian.
"I wish to pay tribute to Neil, who was an infectiously charismatic and fascinating man," leader David Seymour said in the statement.
"He was a dedicated member of the Act Party who will be immensely missed.
"We ask that media respects his family's request for privacy and allows them to mourn in peace."
The Electoral Commission said electorate votes for Port Waikato would no longer be counted, and a by-election would be held after the general election, as set out in the Electoral Act.
However, people were encouraged to still vote, as their party votes would still be counted.
The commission's chief electoral officer Karl Le Quesne extended condolences to Christensen's family.
"Our thoughts are with the family at this difficult time," Le Quesne said.
"It is an unusual situation for a candidate to pass away before election day, and the Electoral Act sets out what happens next," he said.
"Party votes in the Port Waikato electorate will be counted in the General Election results. Port Waikato electorate votes will not be counted, and a by-election will be held after the election to elect a member of Parliament."
The date for the by-election will be set by the current prime minister, Chris Hipkins.
The change appears likely to benefit the National Party, because an extra list seat will be added to make up for the lost electorate seat in the election.
The Port Waikato electorate seat will then be added to the Parliament after the by-election, meaning 121 seats overall - barring any additional overhang seats - and is likely to then be won by incumbent, National's Andrew Bayly.
At 15th on National's list, Bayly is all but guaranteed to make it back in on the list during the election, so the party would be able to bring in another MP from its list.
Bayly won the seat in 2020 with 39.4 percent of the vote compared to the 28.5 percent for Labour's Baljit Kaur. A further 21.3 percent of the vote was taken by Mark Robert Ball from the Heartland New Zealand Party.
