Five hours after the launch of the online booking platform, more than 250,000 people in Hong Kong had registered to travel to China, the government said.

The total number of travellers daily could be higher than 120,000 as residents heading home from both sides will be allowed to cross without booking a quota spot, amid concerns about the risk of infection from a surge of travellers from the mainland who will not be required to produce proof of vaccination.

However officials gave a public assurance that the risks were manageable as a 48-hour polymerase chain action (PCR) test result would still be required as a key component of the new arrangements.

Normal travel over the border has been suspended for almost three years, with only a few thousand permitted to cross each day, compared with an average of roughly 200,000 to 300,000 each day before the pandemic struck.

The loss of mainland tourists helped to push the city into recession, and in announcing the details of the first phase of the reopening, Lee predicted a significant boost to the economy as activity in retail, tourism and transport picked up.

From Sunday, 50,000 travellers a day will be allowed to use the land checkpoints at the Lok Ma Chau railway station, Man Kam To and Shenzhen Bay Port, although they will have to register for a spot first online.

An equal number of places will be available to those seeking to go from the mainland into Hong Kong, and the reservation system will be operated by the Shenzhen government.

But the quotas will not apply to travellers entering the mainland via the airport, two ferry terminals and the Hong Kong-Zhuhai-Macau Bridge, traffic that the government estimated will amount to about 10,000 people a day initially. Neither will the system track residents making the return journey home in either direction.

At the border, successful quota applicants must produce a negative polymerase chain reaction (PCR) test taken within the past 48 hours, although they are required to fulfil any vaccination requirements, despite a proposal earlier made by health minister Lo Chung-mau that mainland visitors should be fully jabbed.

Lee argued that since the changes were “so big”, it would be better not to adjust too many requirements at once.

The PCR test requirement would allow the government to manage risks, while the city’s barrier against the virus was already substantial due to the high vaccination rate and nearly 2.5 million people having already been infected, he said.

The city on Thursday recorded 18,422 infections, including 164 imported ones, and 68 more deaths. The Covid-19 tally stands at 2,720,255 cases, with 12,149 fatalities.

Health chief Lo sought to reassure the public the risk of a surge in infections was low, and said pandemic advisers believed the city’s latest wave had peaked.

“Our public healthcare system has been coping very well, even though we are under pressure,” he said. “With the collaboration of private and public services, we are now ready to cope.”

Visitors would still be sent to isolation if they tested positive, and non-locals must “pay in full” if they sought treatment at public hospitals, he added, stressing service for residents should remain unaffected.

Any mainlanders coming to Hong Kong to take the BioNTech bivalent dose targeting Omicron, which was not available over the border, should seek the shots at private institutions, as free ones offered at government-run centres were only for residents.

Lo estimated that 100,000 PCR tests would be conducted by residents each day in order to fulfil the cross-border requirements. They, alongside visitors, could use 85 testing centres across the city, with the price of each screening capped at HK$150 (US$19) and results ready within 24 hours, according to the government.

The minister also said the government had reserved enough paracetamol for five to six months of usage, but for the first time said authorities would not rule out regulating the purchase and sales of drugs.

Meanwhile, people travelling to Macau from the mainland, Hong Kong and Taiwan will no longer be required to obtain a negative PCR test result beforehand, local authorities announced.

Lawmaker Michael Tien Puk-sun said he expected a total of 100,000 people would travel north each day, once mainlanders returning home were included, although he expressed concerns over the decision not to include a vaccination requirement in the first phase.

Medical experts, however, said PCR tests would be sufficient in preventing imported cases and argued the city had already developed sufficient protection through vaccination and past infections.

“Our herd immunity is able to slow down local transmission. Even if there are imported cases, it would not easily cause local transmission,” said respiratory medicine expert Dr Leung Chi-chiu.

Hong Kong flag carrier Cathay Pacific Airways said it would more than double its flights to the mainland, operating 61 return flights per week between Hong Kong and 13 cities over the border from January 14.

Johannes Hack, president of the German Chamber of Commerce Hong Kong, said it made sense to start with a quota system to “get a feel for how travel flows will develop”.

The chief executive said he would open more checkpoints and increase the quota gradually if the situation allowed, while authorities have allowed cross-border students to return to in-person classes after the Lunar New Year holiday without the need for pre-registration.

The high-speed rail service in West Kowloon, which was suspended in January 2020, would only reopen by January 15 the earliest, officials said, as departments needed more time for drills to ensure smooth operation.

Starting from Sunday, about 10 daytime services from the Hong Kong-Macau ferry terminal in Sheung Wan would be provided every day, a spokesman said.

Macau ferry operator TurboJet said it would resume routes between Hong Kong and the terminal at Taipa, providing 16 daytime rides daily in the initial stage. Tickets will be available from Friday at midday.

Another operator, Cotai Water Jet, will also resume services on the same day with six services in the daytime between the same terminals daily.

Additional reporting by Elizabeth Cheung, Laura Westbrook and Danny Mok