Hong Kong will prioritise testing groups deemed at high risk of contracting the coronavirus, including the elderly, as the first group of medical experts arrived from mainland China to help with free screening of every resident in the city.

The assistance comes as local authorities battle the most severe wave of infections yet, with another 115 emerging on Sunday and two elderly men dying, taking the number of fatalities to 35. But none of the latest cases came from outside the city, a first in six weeks.

Financial Secretary Paul Chan Mo-po warned the “really worrying” surge in infections was taking a toll on the economy, which was already suffering after slipping into its first recession in a decade last year and contracting sharply during the first six months of 2020, against the previous first half.

Officials would continue to work hard to support people struggling amid the downturn, while the government could take lessons from mainland authorities in successfully handling the health crisis, he said.

“The mainland’s epidemic control and prevention strategies have achieved remarkable results,” Chan wrote on his blog. “Many cities have ‘cleared’ all confirmed cases, asymptomatic infections and close contacts requiring medical supervision, allowing people to resume their daily lives.”

The mainland team comprising seven experts was greeted by health minister Professor Sophia Chan Siu-chee and mainland affairs chief Erick Tsang Kwok-wai at the Metropark Hotel in Kowloon where they will be staying. Another 60 medical staff are scheduled to follow. All were selected by the Guangdong Provincial Health Commission from over 20 public hospitals, according to state broadcaster CCTV.

They will help local authorities carry out a pledge made by Beijing to test all 7.5 million residents and bolster processing capabilities, as well as build another makeshift hospital. Work on establishing a new laboratory would begin on Monday, according to a government spokesman.

He dismissed fears mainland personnel would send residents’ DNA information to the mainland.

“We condemn those who deliberately spread false rumours to attack the government’s anti-epidemic work,” he said. “As to whether it would constitute a crime for spreading false rumours, relevant government departments will carefully study and collect evidence for follow-up.”

Sophia Chan said testing priority needed to be carefully researched. “For example, we are worried about the staff and elderly in care home centres in which there may be a need for a second test,” she said.

Health authorities earlier introduced targeted testing for four high-risk groups, including taxi drivers and elderly care home employees. Since the measure was introduced last month, more than 100,000 samples had been collected, according to Chan.

With the assistance of mainland authorities, the government is planning to carry out more than 400,000 additional tests focusing on people with jobs that put them in frequent contact with the public, such as supermarket staff, workers with social welfare groups and others employed in public transport, according to a source.

Hong Kong has confirmed triple-digit daily increases for 12 straight days, with the latest cases pushing the total to 3,511. Of the latest infections, 36 were untraced, while none were imported, the first time arrivals have not contributed to new infections since June 16. Under measures that took effect last Wednesday, aircrew must take a virus test before they fly and have proof of a negative result, while ships without any cargo trade via the city are no longer allowed to make crew changes during their stop.

The new infections were mostly related to gatherings of friends and families, while a cluster tied to a store operated by Star Global, an online retailer with physical outlets across the city, grew to 32.

Health authorities registered four cases at a general ward at the Caritas Medical Centre, but preliminary investigation found the patients were not infected within the hospital.

The two fatalities were a 94-year-old patient with chronic diseases and a 88-year-old man who died last week but whose preliminary positive result was only just confirmed.

The city is planning the construction of a second temporary hospital with the help of a six-member team from Wuhan, where the first Covid-19 cases emerged in December, due to arrive soon. The facility, which can provide up to 2,000 beds, will be similar to the “fangcang hospitals” rapidly constructed to handle Covid-19 patients when the Hubei province capital was struggling with the pandemic.

That team will consist of four medics and two construction specialists, including the president and vice-president of a fangcang hospital in Wuchang district. Mainland media said the team might stay in the city for half a year, mainly assisting with building the facility and not treating patients.

Chan said the temporary facility would be build from scratch to complement a makeshift facility at AsiaWorld-Expo to cope with jump in infections, which has stretched health care facilities to the limit.

It was not clear how long construction would take, she said. Officials must confirm the location and discuss planning with the team from Wuhan.

The experts will start working at the makeshift hospital set up at AsiaWorld-Expo, which is now admitting patients with mild symptoms. About 31 patients arrived on Sunday. But on its second day of operation, one woman was mistakenly admitted to the facility, despite never testing positive for the coronavirus. Throughout the stay, she was in her own ward and did not have contact with other patients, the Hospital Authority said.