Beijing has entered a critical period of epidemic control and prevention work with the city having registered nearly 200 COVID-19 cases in the latest outbreak since April 22, a senior official said on Thursday.

"Some insidious transmissions are still going on at the community level," Pang Xinghuo, deputy director of the Beijing Center for Disease Prevention and Control, said at a news conference on Thursday.

The city reported 53 new locally transmitted confirmed cases and three new asymptomatic carriers between 3 pm on Wednesday and 3 pm on Thursday. The city's total infections hit 194 since Friday and involve 12 districts, according to the center.

After the preliminary analysis of 171 infections that have clear transmission chains or transmission relations, nearly half of them got infected due to dining together, Pang said.

"Among those who dined out, there are two clusters that have caused large scale infections. One is a restaurant in Fangshan district, which has caused more than 50 infections. The other is a fast-food restaurant in Chaoyang district. One of the diners was a teacher who had later spread the infection to students and parents," she added.

The authority has asked all restaurants to strengthen disinfection measures and control the number of people dining at the same time.

All restaurants in controlled zones have been instructed to suspend dine-in service and adopt takeout deliveries only.

As of Thursday, Beijing had five high-risk areas for COVID-19 and 19 medium-risk areas.

On Wednesday, Pang said a big percentage of infections during this outbreak are from schools and kindergartens, involving six schools and two kindergartens by then.

Li Yi, spokesman of Beijing's education commission, said on Thursday that all the kindergartens, primary and middle schools will break for the May Day holiday a day earlier than was previously scheduled.

After the holiday, the authority will decide the date that schools can reopen based on the epidemic situation, he said.

"Students and parents should not leave Beijing if it's not absolutely necessary," he said. "All teachers and students, as well as parents, should not go to parties or get-togethers to avoid infection risks."

During the news conference, Wei Bin, an official from the city government, said Beijing Jiankangbao, a mobile-based app used to check health codes and provide nucleic acid testing services during the COVID-19 epidemic, was attacked by overseas hackers on Thursday.

"Beijing Jiankangbao was attacked on Thursday morning during a peak period. A team of technicians have fixed the problem swiftly," Wei said. "The team later found out that the source of the attack was from overseas."

Wei said during the 2022 Beijing Winter Olympics, the app had also been attacked by overseas hackers.

According to the city authority, the app had been used more than 13 billion health condition inquiries as of February this year.