KAMPALA (Reuters) - Flash floods in Uganda's capital Kampala killed at least three people on Friday and washed away scores of houses, shops and vehicles, witnesses said.

Heavy overnight rains poured into low-lying Zzana slum by the road to Entebbe Airport, submerging some areas.

"It's ruined us," said James Mobza, 30, as he stood in front of a brown lake engulfing rows of shops, a freight truck, a minibus and five cars.

"I saw a woman who died. A man was carrying her but he fell and she was swept away. They fished her body out there," he added, pointing to a chocolate-coloured pool swilling with plastic bottles, flip-flops and polythene bags.

Witnesses said two young children also drowned after falling off the back of their father's motorcycle.

In the slum, residents waded knee-deep through sludge to place belongings they had rescued -- clothes, plates, jerry cans -- on piles of bricks. Iron-roofed shacks lay in ruins. Brick houses were submerged up to their door handles.

"Welcome to Africa," shouted one woman from inside a half-collapsed shack, as she scooped murky water into a wash basin and tipped it out front. "You like the way we live here?"

Two students waded past carrying a desktop computer. "It's spoiled," said one of them.

Residents said President Yoweri Museveni made an impromptu stop at the scene, en route to the airport. But they said he just lectured them for using plastic bags that block drains.

Like other countries across east and west Africa, Uganda has suffered recent floods, swamping villages and destroying crops.

Officials say Kampala's floods are caused partly by people illegally draining wetlands around Lake Victoria to build homes.

Wetlands act like a sponge, soaking up rain. Zzana backs onto a swamp.

"Our problem is people diverting the waters to build on these swamps," said local councillor Moses Senono. "We've been begging the government to stop them."

(Editing by Daniel Wallis)