Indonesia has begun a campaign to vaccinate 6.4m children against polio in two days.
Millions of children will receive the vaccine in one day
The country is suffering its first outbreak of the disease for nearly a decade, with 16 cases reported so far.
The disease, spread by contaminated water, is incurable and causes paralysis and sometimes death.
Officials believe the outbreak can be traced to Nigeria, where vaccinations were suspended in 2003, after radical clerics said they were a US plot.
DNA tests done on a viral sample from one of the infected children has determined that the polio arrived in Indonesia via Saudi Arabia.
Indonesian officials say the virus could have been picked up by a pilgrim on the hajj to Mecca, or a migrant worker.
Polio is still endemic in six countries - Afghanistan, Egypt, India, Nigeria, Niger and Pakistan.
The United Nations has been campaigning to eradicate the disease by the end of this year.
Indonesia first detected a case in West Java province, 120km (75 miles) east of the capital, Jakarta, last month.
Children in villages in the area have already been vaccinated. Polio vaccination rates across Indonesia as a whole stand at about 90%, but in western Java the rate has been around 55%.
"This is important because I don't want my child to be disabled like the ones I see on television," said Nasah, 21, told Reuters news agency, as she brought her 3-year-old son Septyan to a vaccination station.
The vaccine is administered in liquid form, with two drops being squeezed into each child's mouth.
"The people have been very enthusiastic so far today. The health centres are crowded," Dr Muhammad Nadirin, a health ministry official, told the AP news agency.
He said a second round of vaccinations would take place next month.