Wellington - New Zealand's biggest city, Auckland, was warned Friday to prepare for what meteorologists said could be one of the worst subtropical storms to hit the country in a decade.

"This is no ordinary storm," a Meteorological Service spokesman said. "It's one of the largest and deepest lows we've seen for some years.

"By the time this system reaches northern New Zealand on Saturday, it is likely to have significant destructive potential. It is going to deepen rapidly and has the potential of bringing damaging winds, flooding rains, big seas and strong rip tides."

Civil Defence announced it was putting emergency staff on alert Saturday, and police warned people to delay unnecessary travel, keep pets indoors and if possible to lift the city's thousands of pleasure boats out of the water and to safety from winds forecast to hit 120 kilometres an hour.

More than 1 million people, about one-third of the country's total population, live in the Auckland area.

Forecasters said the storm could affect most of the North Island down to the capital, Wellington, 660 kilometres to the south. (dpa)