Texas national guard soldiers aid residents in heavily flooded areas. Photograph: Handout/Reuters

As coastal Texas cleaned up from Harvey, which made landfall as a category 4 hurricane on Friday night before weakening, the storm shifted its attention inland. Amid predictions that as much as 50in of rain could fall, waters rose so high that people were advised to climb to their roofs rather than take refuge in attics, unless they had “an axe or means to break through”.

Heavy rains were predicted to linger for several days and the National Weather Service (NWS), issuing a flash flood emergency warning, said “catastrophic flooding in the Houston metropolitan area is expected to worsen and could become historic”.

More than 6.5 million people live in the region. Several deaths were reported. Early in the day Harris County sheriff Ed Gonzalez reported on Twitter that a woman and child had died in a submerged vehicle on Interstate 10. The deaths were not confirmed, because the location was unreachable. Texas governor Greg Abbott later told CBS he was “not capable at this time of confirming” the number of fatalities caused by the hurricane.

Harvey made landfall on the Texas coast on Friday night with 130mph winds, the most powerful hurricane to hit the US since 2004, and wrought destruction on Corpus Christi and the small towns of Rockport and Port Aransas. At least one person died in Rockport and more than 300,000 lost power. The storm weakened to a category 1, then tropical storm status. But rotating bands of rain began to pummel the Houston area, some 200 miles north-east.

Houston is one of the country’s most flood-prone cities, with thousands of homes on floodplains and next to bayous and creeks. The city endured severe storms in 2015 and 2016 that caused loss of life and widespread damage. Harvey’s effects are likely to be worse.

The city is also home to large oil industry facilities, dangerously vulnerable to flooding. On Sunday, ExxonMobil, Petrobras and Shell said they were shutting refineries in the area and Chevron Phillips said it was shutting its Cedar Bayou petrochemical complex.