MP Judith Collins is the first candidate to put her name forward for the National Party leadership.
She tweeted today: "I'm announcing my candidacy for Leader of the NZ National Party."
"We're going to need strong & decisive leadership if we’re going to win in 2020. I'm that person."
The Papakura MP is considered one of the possible front-runners to replace leader Bill English, who on yesterday announced he would be leaving parliament in two weeks.
National MP Simon Bridges, meanwhile, has also hinted he may soon be announcing a run.
"At the moment I am talking to colleagues," Mr Bridges told media as he arrived at parliament on Wednesday morning.
"We'll just see what happens. It may be that I have more to say later today."
The member for Tauranga was not at Mr English's resignation - unable to make it to Wellington due to weather grounding flights.
Meanwhile veteran MP Nick Smith was staying tight-lipped about the race on Wednesday while Otaki MP Nathan Guy and Auckland Central's Nikki Kaye have ruled themselves out.
Mr English also wouldn't comment on his possible successors.