* 17 people infected in new COVID-19 cluster
* Officials say genome testing suggests U.K. or Australian strain
* Concerns about impact of an extended lockdown on economy
* Ardern still to decide whether to delay general election (Recasts and updates with comment on economy)
By Praveen Menon
WELLINGTON, Aug 14 (Reuters) - New Zealand Prime Minister Jacinda Ardern is due to announce on Friday whether a lockdown in its biggest city will be eased or extended, as officials said it appeared the country's first outbreak in more than three months was an imported strain.
Ardern put Auckland, home to about 1.7 million people, into lockdown on Wednesday, just hours after a four new COVID-19 cases were discovered in a family living in the city. She also reinstated social distancing measures across the country.
A further 13 infections have since been confirmed and linked to the Auckland family, raising some doubts over Ardern's eradication strategy for the pandemic as she heads into a general election next month.
Health Minister Chris Hipkins said on Friday that genome testing of the strain of COVID-19 contracted by the Auckland family suggested it had originated in Britain or Australia.
However, he said how the Auckland family had acquired it was still under investigation, countering comments from Deputy Prime Minister Winston Peters late on Thursday that a quarantine facility breach had been identified as the source.
"People talking about the border, even that's premature at this point, we simply do not have enough information to make even an educated guess about where this may have come from," Hipkins told broadcaster 1NEWS.
Health officials said earlier in the week they were looking into the "low possibility" the virus was imported on frozen food packages. Ten of the new casess have been linked to a cool store that takes imported frozen goods from overseas.
Some prominent local health experts suggested it was more likely the virus had been quietly spreading in Auckland for weeks, despite Ardern's efforts to eradicate it with an initial five-week hard lockdown.
The main opposition National Party has blasted the government, saying it failed to secure quarantine facilities and accusing it of withholding information about the latest outbreak.
New Zealanders celebrated when Ardern appeared to eliminate community transmission of the coronavirus with the earlier hard lockdown that forced almost everyone to stay at home.
But opinion is divided on whether the 40-year-old leader should repeat that strategy, given its huge economic cost and mounting global evidence that the virus cannot be permanently suppressed.
Westpac Banking Corp estimated the current level of lockdown measures in Auckland and the rest of New Zealand would cost the economy about NZ$300 million, or 0.5% of gross domestic product.
Reserve Bank of New Zealand Deputy Governor Geoff Bascand told Reuters a sustained resurgence of the virus posed "a major risk" to the bank's outlook, given its baseline scenario has an assumption that the virus is contained in the country.
Ardern is expected to announce her decision on lockdown measures at 1730 local time (0530 GMT) after meeting with her cabinet and the release of the daily infection numbers. She has said she will make a decision by Sunday on whether to postpone the Sept. 19 election. (Reporting by Praveen Menon; editing by Jane Wardell)