Fatigue and shortness of breath still afflict many patients a year after their hospitalisation for Covid-19, according to a new Chinese study calling for a better understanding of the pandemic's long-term health effects.

Around half of patients discharged from hospital for Covid still suffer from at least one persistent symptom -- most often fatigue or muscle weakness -- after 12 months, said the study published in British medical journal The Lancet Friday.

The research, the largest yet on the condition known as "long Covid", added that one in three patients still have shortness of breath a year after their diagnosis.

That number is even higher in patients hit more severely by the illness.

"With no proven treatments or even rehabilitation guidance, long Covid affects people's ability to resume normal life and their capacity to work," The Lancet said in an editorial published with the study.

"The study shows that for many patients, full recovery from Covid-19 will take more than 1 year."

The study followed nearly 1,300 people hospitalised for Covid between January and May 2020 in the central Chinese city of Wuhan -- the first place affected by a pandemic that has since infected 214 million people worldwide, killing more than 4 million.

The share of observed patients with at least one symptom decreased from 68 percent after six months to 49 percent after 12 months.

Respiratory discomfort increased from 26 percent of patients after six months to 30 percent after 12 months, it said.

It found affected women were 43 percent more likely than affected men to suffer from fatigue or persistent muscle weakness, and twice as likely to be diagnosed with anxiety or depression.

But it said 88 percent of patients who worked before their diagnosis had returned to their jobs a year later.

The study adds to previous research that warned authorities in different countries they must be prepared to provide long-term support to health workers and patients affected by Covid.

"Long Covid is a modern medical challenge of the first order," the editorial said, calling for more research to understand the condition and better care for patients who suffer from it.

New Zealand extends national lockdown
New Zealand on Friday extended a national lockdown sparked by a Delta virus outbreak into next week but warned restrictions would last longer in the infection epicentre of Auckland.

The Delta cluster emerged in Auckland last week, ending a six-month run without local transmission that had made New Zealand one of the world's last Covid-free zones.

While there were 70 new cases reported on Friday, taking the total to 347, Prime Minister Jacinda Ardern said there were signs the outbreak would soon peak if stay-at-home orders remained in place.

"We may be seeing the beginning of a plateau in cases," she said.

"Our job is to keep up the hard work in order to bend, and then flatten, the (infection) curve."

Ardern said a nationwide lockdown imposed on August 17 would now continue until August 31.

She said Auckland, where all but 14 cases have been found, and the neighbouring region of Northland, were set to face at least an extra two weeks of hard lockdown.

New Zealand is pursuing a "Covid zero" elimination strategy -- which has resulted in just 26 deaths in a population of five million -- using strict border controls backed by hard lockdowns when any cases do slip through.

Ardern said that from Wednesday areas outside Auckland and Northland would move down a notch to level three on New Zealand's four-tier virus alert system.

Most residents must still remain at home during level three but some businesses such as restaurants and retail outlets can reopen using contactless collection methods.

Ardern said police checkpoints would be set up to ensure there was no travel between Auckland, Northland and the rest of the country.