Prime Minister Jacinda Ardern urged New Zealanders to trust her Covid-19 response Tuesday, as an opinion poll showed her in a commanding position ahead of the October 17 general election.

In the first televised debate before the vote, Ardern said she stood by a virus programme that has limited the outbreak's toll to 25 deaths in a population of five million. "I know there is a huge amount of uncertainty right now. That's why a plan is necessary, so is optimism, that's what Labour will bring," she said.

Judith Collins, who leads the main opposition National Party, said Ardern's government had failed to secure New Zealand's borders. The TVNZ/Colmar Brunton poll put Ardern's centre-left Labour Party at 48 percent, well short of the record 59 percent it enjoyed in mid-May but enough to retain power with minor party support.

The conservative National Party was on 31 percent, down one percent, while a range of minor parties showed small increases in support. Ardern's backing as preferred prime minister was steady at 54 percent, while nearest challenger Collins dipped two points to 18 percent since the last poll in late July.

Ardern, 40, rose from political obscurity to win the last election in 2017 with support from minor coalition parties. She won international praise for her empathetic and decisive response to last year's attack on two Christchurch mosques by a white supremacist terrorist, in which 51 Muslim worshippers died.

Ardern also implemented tough lockdowns when then the coronavirus pandemic erupted, which health experts say has helped contain the virus. Collins has endured a rocky start after taking over as National's fourth leader since the 2017 election and its third this year.

The centre-right party has campaigned hard on its economic management credentials but admitted over the weekend it made a NZ$4.0 billion (US$2.7 billion) mistake in its tax policy. Collins dismissed the blunder as "inconsequential".