Chinese authorities issued an alert to officials nationwide Saturday to control an outbreak of a virus that has killed more than 20 children and shows signs of spreading.

The alert came after authorities said an 18-month-old boy who died Friday in southern China probably succumbed to the intestinal virus that has killed 22 children in the eastern province of Anhui.

The World Health Organization said Friday that Chinese authorities had taken steps to halt the spread of the the virus, known as enterovirus 71, or EV71, in Anhui.

The U.N. agency said local authorities had improved monitoring of drinking water and provided additional training to healthcare workers.

Xinhua said an investigation is under way into the appearance of the virus in Guangdon.

The WHO says the outbreak of EV71 began in early March, but the number of people hospitalized has jumped since April 19.

The outbreak in Anhui's Fuyang City was not reported until last week.

Xinhua says the outbreak has sickened more than 3,300 children since March.

The news agency said Friday that nearly 1,000 remain hospitalized, 48 of them in serious condition.

Symptoms include fever, blisters, ulcers in the mouth, and rashes on the hands and feet.

Nearly all of the cases have been among children younger than six, with most under two.

WHO says there is no vaccine for EV71, which can be spread through contact with mucus, saliva or feces.

Outbreaks have been reported in Singapore, Taiwan and Malaysia. An outbreak of the virus in Taiwan in 1998 killed 78 children.

Some information for this report was provided by AP and Reuters.