JAKARTA, Indonesia — Boats carried emergency supplies to desperate residents of Indonesia’s flood-stricken capital yesterday as overflowing rivers again burst their banks following days of rain. At least 20 people have been killed and almost 340,000 others made homeless, officials said.Hundreds of people remained on the second floors of their houses, either trapped or unwilling to abandon them despite warnings that muddy water running four meters deep in places may rise in the coming days.

“Jakarta is now on the highest alert level,” said Sihar Simanjuntak, an official monitoring the water levels of the many rivers that crisscross the city of 12 million people. “The floods are getting worse.”

The government dispatched medical teams on rubber rafts into the worst-hit districts amid fears that disease may spread among residents living in squalid conditions with limited access to clean drinking water.

Edi Darma, an official at Jakarta’s Flood Crisis Center, said the death toll from flooding in Jakarta and surrounding towns had reached 20 as of late yesterday, mostly either by drowning or electrocution.

“We were starving for two days,” said Sri Hatyati, who was rescued from her house by soldiers on a dinghy yesterday on the city’s western outskirts. “All we had were dried noodles. We were unable to go anywhere.”

Incessant rain over Jakarta and hills to its south from Thursday triggered the city’s worst floods in recent memory, inundating tens of thousands of homes, school and hospitals in poor and wealthy districts alike.

Authorities have cut off electricity and the water supply in many districts.

Dr. Rustam Pakaya, from the health ministry’s crisis centre, said nearly 340,000 people had been made homeless, many of whom are staying with friends or family or at mosques and government buildings.

“We fear that diarrhea and dysentery may break out, as well as illnesses spread by rats,” Pakaya said. “People must be careful not to drink dirty water.”

There was little rainfall over Jakarta yesterday, but fresh flooding occurred as heavy downpours over the southern hills in Puncak caused rivers to swell across the city, prompting authorities to open flood gates.

An Associated Press photographer saw Red Cross officials ferrying water and food to people cut off by the floods in downtown districts. TV footage showed people standing on roofs, and cars overturned.

Indonesia’s meteorological agency is forecasting rain for the next two weeks.

Environment Minister Racmat Witoelar blamed poor urban planning for the disaster.

“Authorities hand out (building permits) even though they clearly violate environmental impact studies,” The Jakarta Post newspaper quoted him.

Jakarta Governor Sutiyoso, who was criticised when massive floods struck the city five years ago, blamed widespread deforestation in Puncak, saying it had destroyed water catchment areas.

Seasonal downpours cause dozens of landslides and flash floods each year in Indonesia, a sprawling archipelago of 17,000 islands, where millions of people live in mountainous areas or near fertile plains.