Judith Collins, Amy Adams and Simon Bridges have announced they are all in the running to be next leader of the Opposition.
Ms Adams said there needs to be a plan to get things done.
"We are going to be committed to holding this Government to account," she said.
Ms Collins says she brings strength while Mr Bridges says he offers generational change.
Jonathan Coleman and Mark Mitchell could also be in the running.
Meanwhile, Paula Bennett has ruled herself out of gunning for the leadership. She wants to ride shotgun as deputy leader.
National Party leadership contest - Who's in?
- Judith Collins - Has officially announced her bid
- Simon Bridges - Has officially announced his bid
- Amy Adams - Has officially announced her bid
- Mark Mitchell - Strongly hinting at running
- Jonathan Coleman - Considering running
- Paula Bennett - Ruled herself out of leadership, wants to remain deputy
- Nikki Kaye - Ruled herself out
- Maggie Barry - Ruled herself out
- Nathan Guy - "I won't be running"
- Alfred Ngaro - Ruled himself out
The first keen candidate to announce their bid was Ms Collins, via Twitter on Wednesday morning.
"We're going to need strong & decisive leadership if we're going to win in 2020," Ms Collins said.
"I'm that person."
She was followed by Mr Bridges, who announced he's running for leadership at Parliament on Wednesday morning.
He said as a 41-year-old with a young family, he balances generational change with experience.
"We will need to continue to evolve. We do need to have fresh ideas," he said.
'We've got a top team. We've got a Government that can seriously challenge and hold to account... But you've got a complete package that is an Opposition that has a very clear sense of what we're about."
Ms Adams made her announcement outside Parliament on Wednesday afternoon. In a show of support, she was joined by colleagues Chris Bishop, Nikki Kaye, Maggie Barry and Tim Macindoe.
Ms Adams offered some detailed answers on issues facing New Zealand. On climate change, she said it's an important issue that "should not be subject to a three-year term" and that farmers could use technology to find solutions to environmental problems.
Describing herself as a candidate, Ms Adams said "the compassion, integrity and life experience... makes me somewhat unique".
She said she is socially liberal but fiscally "right in core National territory."
Ms Collins told The AM Show she believes she has "strong" support.
"I was approached by several colleagues to stand over Christmas break."
However, she says it's not something she considered until Mr English resigned on Tuesday - adding she's not in it for herself.
"I'm not foolish enough to think leader of the Opposition is anything other than the toughest job in politics.
"But you know what? It needs someone who's tough. I'm ready for it.
"I'm not frightened of questioning what the Prime Minister does, and I'm very relaxed in holding her to account.
"We've got to get into a much higher gear in opposition."
While Ms Collins wants the role of leader, Ms Bennett wants to keep her current job - deputy leader.
Writing on Facebook, Ms Bennett said she will not be seeking leadership. "I believe it's my role as deputy where I have the most to add. Our new leader will need help from an experienced, loyal deputy and I offer that."
Meanwhile, Nikki Kaye has ruled herself out of both leader and deputy positions.
Mr Bridges was not at Mr English's resignation announcement. He was stuck in Tauranga as flights out have been cancelled for the past couple of days.
But on Wednesday morning he told Newshub it's been an "interesting 24 hours".
"I think the vast majority of my colleagues didn't know this was coming.
"So it was very surprising."
Mr Bridges threw his hat in the ring for the deputy position during the last leadership contest but was unsuccessful.
Jonathan Coleman, also tipped as a potential candidate, didn't give any clues away.
"There's a long way to go in this," Mr Coleman told Newshub.
"I'm not ruling anything in or out.
"[I'm] just seeing what's happening. There was no real discussion yesterday by the caucus.
"The key thing is National can win in 2020 and that's what we've got to be focused on."
Mr English is staying tight-lipped about who he thinks should replace him.
"I'm sure they'll pick a capable leader who will do that job, and we'll go off and have a new life," he told The AM Show.