A 5.7-magnitude earthquake shook the New Zealand capital and the north of the country's South Island at 7:19 p.m. Saturday.

The government-run GeoNet monitoring service reported the quake was centered 30 km east of the port town on Picton, at the north of the South Island, and occurred at a depth of 60 km.

There has been no serious damage, but a number of windows on a waterfront building in Wellington were broken, the Radio New Zealand quoted the police and the fire service as saying.

Dr Tony Hurst, from the GNS Science research institute, told the Radio New Zealand that the quake would have been widely felt because it was relatively high magnitude and occurred deep in the earth crust.

He said it was felt quite strongly right out to Golden Bay, on the far north-east of the South Island, and even to south Taranaki, in the central North Island.

The epicenter was very near Fighting Bay, starting point of the Cook Strait cable carrying electricity between the North and South islands, but power company Transpower said it was not damaged, according to the report.

The Fairfax news service reported that the GNS had confirmed it was the biggest earthquake in the South Island's Marlborough region since a quake near Seddon, south of Blenheim, in 1966.

The region is a popular tourist destination renowned for its picturesque coastlines and vineyards.

Residents in the capital reported crockery and ornaments being rattled and broken, while workers in central Wellington office buildings took cover under their desks.

Cafe customers in Picton ran out into the streets, according to reports.

Sharon Hitch, manager at Picton Top 10 Holiday Park, told Fairfax she and her husband had taken cover under doorways as the quake was the biggest they had felt for a number of years.

"It was a bit of a shaky one. The buildings weren't moving that much but the earth was definitely shaking. It was hard to stand still," she said.

Hitch was reported as saying she felt the quake lasted for at least 20 seconds.

New Zealand is currently on a high alert for earthquakes as hundreds government buildings are being assessed for risk from tremors.

An Inland Revenue processing centre in Wellington's Upper Hutt housing hundreds of staff is to be closed for a month and six court buildings - three in the lower North Island - would be closed for up to a year for earthquake strengthening work, the Dominion-Post newspaper reported Saturday.

Forty schools in Wellington city were deemed potentially earthquake-prone or were under investigation, said the report.

In February, a 6.3-magnitude quake struck New Zealand's second city of Christchurch, leaving at least 181 people dead.