It warned that the number of deaths could rise because of cross-infections, bad weather and overcrowding at paediatrics hospitals in major cities where panicked parents are bringing their infected children.

Vietnamese Prime Minister Nguyen Tan Dung on Wednesday called for authorities to be more "active" in preventing the spread of the disease.

The authorities are providing vaccines, stepping up surveillance of the disease and urging parents to seek treatment locally instead of at paediatric hospitals whose patients are vulnerable to infection.

World Health Organisation representative Takeshi Kasai said he was "very concerned" about the outbreak.

"This virus is very infectious and difficult to control," he said, adding that the best way to contain the disease was to encourage people to be vaccinated.

Vietnam has high rates of vaccinations for many early childhood diseases including measles, but may be falling victim to its own success as some parents - particularly those who have read scare stories about vaccination side effects - perceive less risk from leaving their children uninoculated.

Nguyen Hoa Lan, 38, said both her son and daughter - aged 10 and 7 - have become infected with measles in the last week.

"I am worried as I only vaccinated my daughter once... I forgot the second vaccination. But also because of scandals and rumour with the vaccination, I decided to skip it. Now it makes me worried," she said.

"I can only pray that things will be OK."

Measles, a highly contagious viral disease which is particularly deadly for young children, claimed about 122,000 lives globally in 2012, the most recent year for which global figures are available, according to the WHO.

Back in 2000, the toll was a stark 562,000.

The measles vaccination is not particularly effective for children under nine months, the WHO said, so societies need to ensure high rates of vaccination among older children to boost overall immunity of the population.

Agence France Presse - April 18, 2014