TAIPEI - The health authorities in Taiwan have again tightened restrictions as the island reports an increasing number of Covid-19 cases.

On Tuesday (Jan 11), 12 local and 58 imported cases were recorded, a sharp jump from the four and 30 reported on Jan 4.

Like the first Covid-19 wave between May and August last year, the current outbreak is centred on the northern part of the island with clusters reported in Taoyuan municipality where the main international airport is located.

It began on Jan 2 with three infected airport janitors but has now ballooned to a string of cases involving 16 airport staff and 15 other people in the community.

The Taoyuan authorities have suspended classes at two elementary schools that reported one positive case each, and are working to trace and screen potential cases. "The Covid-19 team in Taoyuan has been working non-stop, expanding contact tracing and screening some 20,000 people," said Taoyuan Mayor Cheng Wen-tsan in a Facebook post on Tuesday.

The Central Epidemic Command Centre has dispatched a team of health experts to examine airport hygiene conditions, Health Minister Chen Shih-chung disclosed on Monday.

Previously, the CECC had hinted at lifting quarantine restrictions on Taiwanese, and possibly foreign travellers, entering Taiwan after Chinese New Year, once more than 70 per cent of the population had been fully vaccinated, and if the local transmission rate remained low. But on Sunday, the authorities announced an extension of the Level 2 Covid-19 Alert to at least Jan 24.

In Taiwan's four-tier alert system, Level 2 is implemented when local cases with unidentifiable sources are reported. It requires people to don masks outdoors and limits outdoor gatherings to under 500 people. Indoor gatherings are restricted to under 100 people.

Beginning Tuesday, passengers arriving on flights from Europe, the Americas, the Middle East, Australia and New Zealand must wait for the result of their Covid-19 test before clearing customs.

Those who test positive will be taken in an ambulance to a hospital for treatment, while those with a negative result will be transported to quarantine facilities.

"We're moving the line of defence to the (airport) front line... due to the incubation period for the Omicron variant being shorter. We think a large number of infected travellers will test positive at the airport under the new regulation," said Dr Chen.

The first flight arriving from Sydney, Australia, early Tuesday morning saw four passengers testing positive.

"That's a positivity rate of about 10 per cent, it's higher than we anticipated," said Mr Wang Bi-sheng, a health official directing the testing procedure at the airport.

He acknowledged some discrepancies in carrying out the new protocols, saying there was a need to spread out staff for the testing to accommodate "a large number of flights carrying only a few passengers each" and for more equipment at screening stations.

The health minister has also encouraged Taiwanese to sign up for booster shots. "We have more than eight million doses in stock, I guarantee that there is enough for everyone," he said on Sunday.

As at Tuesday, 70.7 per cent of the island's residents have received both doses of the Covid-19 vaccine, and some 1.12 per cent have had their booster shots.

Last year Taiwan recorded more than 100 cases every day from May 15 to June 20, and the number of daily cases remained in the double digits until early August as the government struggled to procure vaccines.

The vaccine shortage has since eased considerably, and so has the sense of concern among people this time around.

"I'm cancelling a gathering with a friend this weekend just to be cautious, but I'm not too worried this time since all my friends and family are fully vaccinated," said Ms Chih Jia-wei, 31, an administration staff member in the finance industry, reflecting the general mood.

Taiwan has reported a total of 17,463 cases and 850 deaths so far.