New Zealand Prime Minister Jacinda Ardern will stand down on February 7. She said she had hoped to find the energy and heart to continue in the role over summer, “but I have not been able to do that”.

New Zealand's Prime Minister Jacinda Ardern dropped a huge bombshell when she announced her resignation this week.

Among the many questions that come in the aftermath is: Who will take over as Prime Minister? And when?

Ardern herself gave some indications on the latter, at least. Here's what you need to know.

A new PM within days?

Ardern's replacement as leader of the Labour Party will take over as Prime Minister. The party's own process for picking a leader, therefore, is effectively what decides who gets the gig.

The first step, Ardern said, was for caucus to decide within seven days if there was someone within their ranks that at least two-thirds agreed should be leader. Already, the caucus has decided it will establish this via a vote this Sunday.

If someone gets two-thirds of the 65 votes (44 is the magic number) in Labour's caucus, they will become leader.

Ardern indicated she would issue her resignation as prime minister to the governor general "soon after", if that happened. A new PM could, therefore, be in office by early next week.

This will be Ardern and the party's hope. But in reality, the field looks fairly open (Deputy Prime Minister Grant Robertson has ruled himself out as a candidate, as has deputy Labour leader Kelvin Davis) so a two-thirds majority may be hard for any one person to muster. What would happen then?

Read more on RNZ: What you need to know: Who takes over from Jacinda Ardern as Prime Minister when she steps down?