HOUSTON (NYTIMES) - A series of explosions at a flood-damaged chemical plant outside Houston drew sharp focus on hazards to public health and safety from the city's vast petrochemical complex as the region begins a painstaking recovery from Hurricane Harvey.

The blasts on Thursday (Aug 31) at the plant, owned by French chemical company Arkema, came after its main electrical system and backups failed, cutting off refrigeration systems that kept volatile chemicals stable.

While nearby residents had been evacuated, 15 public safety officers were treated at a hospital after inhaling smoke from chemical fires that followed the explosions.

The Arkema plant has been identified as one of the most hazardous in the state. Its failure followed releases of contaminants from several other area petrochemical plants and systemic breakdowns of water and sewer systems in Houston and elsewhere in the storm-struck region.

The explosions - more are expected, the company said - will bring fresh scrutiny on whether these plants are adequately regulated and monitored by state and federal safety officials.

The chemical plant accident came as devastation from Harvey, now a tropical depression moving into the Mississippi Valley, continued to spread across the region. The known death toll from the storm and flooding rose to 39, authorities said.

Record-breaking floods swept through Beaumont, Texas, east of Houston, damaging the water system and leaving the city's 120,000 residents without clean water.

Beaumont city officials said they would not be able to assess the damage to the water system until floodwaters began to recede, and efforts were being made to distribute bottled water. But Harvey dropped nearly 4 ft of rain in the area, and most roads into the city remained impassable.

Vice-President Mike Pence and several Cabinet officials arrived in Corpus Christi, Texas, around midday on Thursday before heading to nearby Rockport to survey the devastation left by the storm, speak with victims and survey the cleanup effort.

Tom Bossert, the official leading the White House's response to the disaster, estimated that 100,000 homes in Texas and Louisiana had been damaged or destroyed, and said that President Donald Trump would soon seek billions in aid.

Bossert said that rescuers would provide aid to the estimated 500,000 unauthorised immigrants in the Houston area and that federal officials would not round up those whose only offense was entering the country illegally.