HOUSTON (Reuters) - Scores of schools were closed and cleanup was underway in Houston on Tuesday, a day after record rains hits the fourth most populous US city, causing floods that left five dead and led to more than 1,000 water rescues.

The National Weather Service has put a flash flood watch in effect for large parts of the Houston area and into southwestern Louisiana on Tuesday. As much as 45cm fell in some areas of Harris County, which contains Houston, and the weather service said heaviest daily rain records were set on Monday at the two main airports in the city.

More storms have been forecast for already saturated parts of Texas on Tuesday. About 9,000 customers were without power in the Houston area on Tuesday morning, a sharp decrease from more than 100,000 a day earlier, CenterPoint Energy said.

Flood waters that blocked roads to downtown and other main areas of the city have largely receded, with officials saying most people should be able to make it back to work.

"The city is back to normal operations but be careful driving in. Now we plan to help people recover from the flooding waters," Houston Mayor Sylvester Turner said in a tweet.

As of 8am CDT (9pm Singapore time), there were more than 100 flight cancellations on Tuesday at Houston George Bush Intercontinental Airport, according to tracking service FlightAware.com.

More than 1,000 flights were cancelled at major Texas airports on Monday due to the storms.

Rains in other parts of the state were expected to cause rivers to crest later in the week, bringing floods to downstream areas, the weather service said.