With China now in peak flu season, authorities have said infections should remain under control, as no mutations that might boost the strength or drug-resistance of the virus have been detected.

However, Beijing has seen a notable increase in infections among children since the start of the month, according to data from the Beijing Center for Disease Control and Prevention.

Those affected are mostly students at primary schools and kindergartens.

"My colleague and I received over 300 patients between 4 am and 8 am on Tuesday," said Zhou Zhongshu, director of pediatrics at the capital's China-Japan Friendship Hospital. "The number of daily patients has increased by over 30 percent to 600 or 700.

"Cross-infection is the main cause of the epidemics, especially at schools and in enclosed areas."

Daily outpatient visits to the pediatrics department of Beijing Children's Hospital have reportedly reached more than 10,000, a record level, while the number of children with respiratory tract infections and high fevers has increased by about 20 percent.

The seasonal flu virus can cause high fever, headache, malaise and cough. Pneumonia, shock or even death could occur if the virus is not properly treated.

Gu Li, a physician with the infectious diseases department of Beijing Chaoyang Hospital, said the flu season usually lasts three months in winter. Most patients get mild infections and will recover after treatment.

However, seniors, pregnant women and children under age 5 are at higher risk, she warned.

Five to 10 percent of adults and 20 to 30 percent of children worldwide are infected with flu every year, killing about 290,000 people, according to the World Health Organization.