By Paulo Prada

RIO DE JANEIRO (Reuters) - Heavy rains late Tuesday and early Wednesday paralyzed much of Rio de Janeiro, a tropical metropolis scrambling to improve infrastructure to prepare to host the 2014 World Cup and the 2016 Olympics.

More rain fell overnight around the city, Brazil's second biggest, than would normally be expected during the entire month, meteorologists said. The downpour flooded major thoroughfares, toppled houses in working class suburbs, disrupted train and flight schedules and created such chaos that Mayor Eduardo Paes asked residents to stay home.

No deaths have been reported, but emergency personnel by early afternoon Wednesday were tending to isolated injuries and evaluating the extent of the damage.

Though December is part of the annual rainy season, the intensity of the rains underscored longstanding concerns about flooding in a coastal city where slipshod development and poor public oversight in past decades led to an urban sprawl across a

floodplain between nearby mountains and the sea.

"We are now dealing with the problems of opportunistic development that puts people and property at risk," said Moacyr Duarte, an engineer and researcher on disaster management who also advises the city on preparedness. "The authorities never should have let much of this to be built."

Television footage and snapshots sent to local media by harried residents showed passengers standing atop buses half submerged in muddy water. One Rio resident was photographed riding a jet ski past another trapped bus, while some motorists were stuck in cars that risked being swept away by rising runoff.

The flooding comes just six months before Rio, along with 11 other Brazilian cities, welcomes hundreds of thousands of visitors for World Cup soccer games. Two years later the city will host the summer Olympics, an event for which it is busy building new venues, bus and rail lines and other facilities.

While local officials pointed to advances since past flooding, when smaller volumes of rain led to deaths, they remain concerned that long-term climate forecasts suggest that downpours will only intensify across southeast Brazil in the coming years.

Long accustomed to hosting throngs of tourists and major events, such as annual Carnival celebrations and a big seaside New Year's party, the city and surrounding region, an area of more than 10 million people, have nonetheless repeatedly been caught off guard by the weather.

Last July, when rains turned a rural field they had prepared for a campsite and outdoor sanctuary into a bog during a high-profile visit by Pope Francis, authorities had to relocate the final mass scheduled. In 2011, heavy rains in the mountains outside Rio caused major mudslides and killed more than 900 people.

Local forecasts predict rain over Rio at least through the end of the workweek.

(Editing by Todd Benson)