Torrential rains have killed at least 15 people in Texas and Oklahoma, including three in Houston where floods turned streets into rivers and led to about 1,000 calls for help in the fourth-most populous U.S. city, officials said on Tuesday.

The death toll is set to rise with numerous people still missing in Texas after the storms slammed the states during the Memorial Day weekend, causing record floods that destroyed hundreds of homes, swept away bridges, and even unearthed a coffin from a Houston cemetery. It washed ashore on the banks of a bayou.

"A lot of folks drove their car into high water and had to abandon those vehicles," Mayor Annise Parker said at a news conference.