New Zealand Prime Minister Jacinda Ardern will step down by next month because she no longer has “enough in the tank” to do the job justice, she said.

“I’m leaving because with such a privileged role comes responsibility — to know when you’re the right person to lead and also when you are not,” said Ardern, who leads the country’s Labour Party and won her first term 5½ years ago.

Ardern, 42, said Thursday afternoon local time (7 p.m. ET Wednesday) she would not seek re-election and planned to resign no later than Feb. 7.

“This has been the most fulfilling 5½ years of my life, but it has also had its challenges,” she told reporters. “Amongst an agenda focused on housing, child poverty and climate change, we encountered a major biosecurity incursion, a domestic terror event, a major natural disaster, a global pandemic and an economic crisis.

“The decisions that have had to be made have been continual, and they have been weighty,” she said.

The party has seven days to determine whether a new leader has more than two-thirds of caucus support, she said. A vote will occur Sunday.

If a new leader is selected, Ardern said, she will resign soon after and a new prime minister will be sworn in. If not, the vote will go to the wider party membership, she said.

Ardern said she plans to remain in Parliament in order to avoid a by-election.

“Beyond that I have no plan, no next steps,” she said. “All I know is whatever I do I will try to find ways to keep working for New Zealand.”

Ardern had faced a tough election campaign this year. Her liberal Labour Party won re-election two years ago in a landslide of historic proportions, but recent polls have put her party behind its conservative rivals.

She was lauded globally for her country’s initial handling of the coronavirus pandemic after New Zealand managed for months to stop the virus at its borders. But its zero-tolerance strategy was abandoned once it was challenged by new variants and vaccines became available.

She faced tougher criticism at home that the strategy was too strict, and many of Ardern’s right-wing critics cheered her resignation announcement.

Ardern announced last month that a Royal Commission of Inquiry would look into whether the government made the right decisions in battling Covid-19 and how it can better prepare for future pandemics. Its report is due next year.