Houston mayor Sylvester Turner said 40 boats would be added for rescuing people from high waters that have filled neighbourhoods and highways. "Don't get on the road. Don't assume this storm is over," Mr Turner said.
Harvey came ashore late Friday as the most powerful hurricane to hit Texas in more than 50 years and has been linked to at least two deaths. The death toll is expected to rise as the storm lashes the US state for days, triggering more floods, tidal surges and tornadoes.