Floodwaters from Tropical Storm Harvey, which has already killed at least seven people in Texas and expected to drive tens of thousands from their homes, will likely rise in the coming days, officials warned on Monday as heavy rains continued to pound the U.S. Gulf Coast.

National Guard troops, police officers, rescue workers and civilians raced in helicopters, boats and special high-water trucks to rescue the hundreds of people still stranded in and around Houston, the nation’s fourth-largest city.

The storm was the most powerful hurricane to strike Texas in more than 50 years when it came ashore on Friday near Corpus Christi, 220 miles (354 km) south of Houston and the worst far from over as the National Weather Service issued numerous flood warnings across the region.

U.S. President Donald Trump

President Donald Trump plans to go to Texas on Tuesday to survey the damage and may in the future visit Louisiana where the storm is now dumping rain.

Trump, facing the biggest U.S. natural disaster since he took office in January, has signed disaster proclamations for Texas and Louisiana, triggering federal relief efforts.

Harvey has killed at least six people in Harris County, where Houston is located, said Tricia Bentley, a spokeswoman for the county coroner’s office, including a man who died in a house fire on Friday night and an elderly woman driving through flooded streets on the city’s west side the next day.

A 60-year-old woman died in neighbouring Montgomery County when a tree fell on her trailer home while she slept, the local medical examiner said on Twitter.

Both of Houston’s major airports were shut down, and most major highways, rail lines and a hospital, where patients were evacuated over the weekend. As of Monday evening 267,000 Texans were left without power in the southeast corner of the state.

Roads flooded

The Harris County Office of Homeland Security and Emergency Management issued a “shelter in place” warning to residents of La Porte and Shoreacres, about 25 miles (40 km) east of Houston, after a chemical leak caused by a ruptured pipeline.

As stunned families surveyed the wreckage of destroyed homes and roads flooded or clogged with debris, Texas Governor Greg Abbott warned Houstonians to brace for a long recovery.

“We need to recognise this is going to a new and different normal for this entire region,” Abbott said.

Harvey expected to linger over Texas’ Gulf Coast for the next few days, dropping another 10 to 20 inches (25 to 51 cm) of rain, with threats of flooding extending into Louisiana.

In scenes evoking the aftermath of Hurricane Katrina in 2005, police and Coast Guard teams have rescued at least 2,000 people so far, plucking many from rooftops by helicopter, as they urged the hundreds more believed to marooned in flooded houses to hang towels or sheets outside to alert rescuers.

Harvey’s centre about 100 miles (160 km) south of Houston and forecast to arc slowly towards the city through Wednesday, with the worst floods expected later that day and on Thursday.

 Schools and office

Schools and office buildings closed throughout the metropolitan area, home to 6.8 million people, as chest-high water filled some neighbourhoods in the low-lying city.

The U.S. Army Corps of Engineers said Monday that it was releasing water from the nearby Addicks and Barker reservoirs into Buffalo Bayou, the primary body of water running through Houston.“The more they release it could go up and it could create even additional problems,” Houston Mayor Sylvester Turner warned.

Torrential rain also hit areas more than 150 miles (240 km) away, swelling rivers and causing a surge that was heading towards the Houston area, where numerous rivers and streams already have breached.

Also read: Hurricane Harvey makes strong landfall in Texas as Category 4 hurricane