Whangarei's National MP Shane Reti, said he heard the news about half an hour before the Prime Minister told the press.
Reti said the decision did not affect his own political aspirations - he remained fully committed to aiming for a second term in the Whangarei electorate.
"We were on a caucus call 30 minutes before [the press conference] and that's when we found out as well," Reti said.
"I was surprised but I appreciated his honesty and I understand the reasons."
AdvertisementAdvertise with NZME.
Reti said there was "quietness on the call" and he could not gauge the mood within National until he met with his colleagues at a meeting planned for tonight.
Te Tai Tokerau Labour MP Kelvin Davis said Key's resignation spelled opportunity for his own party.
"We were ready [for the election] anyway and this makes it a little more interesting," he said.
But it had little bearing on his own electorate, Davis said.
"I have to focus on what I've been doing and highlighting the fact that a lot has been achieved," he said. "We've heard the news, now we're getting on with making sure the people in our electorates are being served."