HANOI -- Vietnam on Friday reported 45 new coronavirus infections in the city of Da Nang, marking the country’s biggest single-day jump in cases, as the health ministry sent more health experts to the central city in a bid to combat the outbreak.

The new patients, aged between 27 and 87, are linked to three hospitals and two clinics in Da Nang, a tourism hot spot where Vietnam last week detected its first locally transmitted infections in more than three months, the ministry said in a statement.

Vietnam started mass coronavirus testing in the capital Hanoi, banned gatherings in its economic hub and urged tens of thousands of domestic travellers to report to authorities on Thursday, as the country scrambled to contain the new spread of the virus.

The ministry overnight sent a special task force of health experts, along with more than 1,000 health workers, to Da Nang to help handle the deteriorating situation there, it said.

The task force includes 65 health experts who had previously helped fight coronavirus at other epicentres in Vietnam, the ministry said.

The newly confirmed cases in Da Nang have brought up the total number of cases in Vietnam to 509, with no deaths.

Some experts say Vietnam could be paying for complacency after its initial success stopping the virus, with normal service quickly resuming, face masks used less and domestic travel activity surging.

Da Nang had been inundated with visitors taking advantage of promotions to revitalise a tourism sector hurt by border closures and international flight bans designed to keep the virus out.

The current wave is traced to Da Nang, but the source is unclear.