Authorities in Houston have warned residents affected by Hurricane Harvey more flooding is likely.

Rescuers have begun a block-by-block search of tens of thousands of Houston homes looking for anyone - alive or dead - who might have been left behind in Harvey's floodwaters.

Latest: Fires and two explosions have rocked a flooded chemical plant in Texas, sending up a plume that federal authorities described as "incredibly dangerous" and adding a potential new hazard to the aftermath of Hurricane Harvey.