KUALA LUMPUR/SINGAPORE -- Southeast Asian governments are bracing as COVID-19 infections are already surging and more foreign tourists pour into the region ahead of the year-end holidays.

Malaysia has reactivated the Heightened Alert System -- an early intervention protocol based on the infection and death levels as well as the hospitalization rate -- to better monitor and appropriately respond to infections. Singapore, Thailand and Indonesia have issued advisories asking people to mask up and get vaccinated.

The number of cases has shot up as much as 75% in these countries since the start of this month, pushing case numbers into the tens of thousands.

Experts say there is no need for lockdowns or border closures this time, noting governments are better prepared, ensuring that economies and businesses will remain open and uninterrupted. At the same time, residents and travelers are being encouraged to do their part to stay safe as they go from gathering to gathering and place to place.

New infections in Malaysia shot up by 62.2%, to 20,696, during the week of Dec. 10 to 16. Of the cases, 97% were mild, though 96 patients were on ventilators and 28 deaths occurred.

The highly infectious omicron variant was predominant.

On Wednesday, the country's health ministry announced it would activate 235 vaccination centers at government clinics to ramp up vaccination coverage. The ministry earlier this week said no lockdowns would be imposed, though authorities are encouraging the public to remain vigilant by wearing masks indoors and getting vaccinated.

Neighboring Singapore has also taken steps after a spike in infections. On Tuesday, the health ministry began a daily update on coronavirus cases on its website "to provide the latest information on the situation during this period of surge in cases."

The additional measures come after the Ministry of Health on Dec. 15 announced infections in the country jumped 75% to more than 56,000 cases in the week of Dec. 3 to 9. It was the third consecutive week of increase.

Following the spike, the health ministry said it "strongly encourages" residents and travelers to wear masks in crowded places and airports even if they are not sick, especially indoors or around vulnerable people.

Experts say omicron sub-variants are driving the spike. The highly infectious mutations generally lead to less severe illnesses than earlier variants. Though they are past their peak, they continue to circulate globally.

Azrul Mohd Khalib, chief executive at the Galen Center for Health and Social Policy in Kuala Lumpur, told Nikkei Asia that ever since different variants and sub-variants began to circulate there have been periodic surges, especially now that global travel has resumed. "The current surge is due to increased movement of people and, most importantly, waning population immunity," he said.

Southeast Asia gradually reopened in 2022, welcoming back tourists. With the relaxation of restrictions fueling tourism and business recoveries, occasional spikes in COVID-19 cases have served as reminders of the pandemic's lingering grip.

In Thailand, new cases now number around 5,000 per day, the highest rate for the past five months, according to the health ministry. Cases have been trending upward since the country in October 2022 fully reopened to foreign tourists, whose prepandemic spending accounted for about 18% of Thailand's gross domestic product.