Indonesian authorities have confirmed a second case of polio, a day after announcing they had discovered the first case for almost 10 years.
Authorities have increased the number of immunisations
Officials said they were confident they could prevent a major outbreak.
Indonesia has begun a programme of vaccinating millions of children in the West Java region, where the disease was first found in an infant girl.
The second case, in the same area, was found in an 18-month-old boy. The virus is thought to have come from Africa.
Polio is a waterborne disease which usually infects young children by attacking the nervous system. It causes paralysis and muscular atrophy, and there is no cure.
Dr Umar Achmadi, head of communicable disease control for the Indonesian health ministry, said officials had investigated the region for further infection in the wake of the first case.
"We found six other cases of paralysis, we confirmed one more additional case, and five turned out negative," he said. "I got the test results this morning."
Polio vaccination rates across Indonesia as a whole stand at about 90%, but in western Java the rate has been around 55%.
Authorities have now launched a drive to immunise five million children in the area.
The infection of a 20-month-old girl, which Indonesia announced on Tuesday, was the country's first recorded case of polio in almost a decade.
DNA tests done on a viral sample from the infant girl has determined the polio arrived in Indonesia from Nigeria, via Saudi Arabia.
Experts suspect the strain could have been carried by migrant workers or pilgrims visiting Muslim holy sites in Saudi Arabia.
Dr Achmadi said he was "99% sure" the same viral strain had affected the baby boy.
The disease has all but disappeared in the developed world, but it is still endemic in Nigeria, a problem that was made worse in 2003 when Muslim clerics there spread rumours that the polio vaccine had been contaminated to make Muslims infertile.
Until the middle of last century, when a vaccine was discovered, polio was endemic across the globe, and the international campaign for universal vaccination has been one of the great successes in the fight against disease of recent years.