HOUSTON (AP) — Officials released more water from Houston-area reservoirs overwhelmed by Harvey early Monday in a move aimed at protecting the city’s downtown from devastating floods but that could still endanger thousands of homes, even as the nation’s fourth-largest city anticipated more rain.

Harvey, which made landfall late Friday as a Category 4 hurricane and has lingered dropping heavy rain as a tropical storm, sent devastating floods pouring into Houston on Sunday. The rising water chased thousands of people to rooftops or higher ground and overwhelmed rescuers who could not keep up with the constant calls for help.

Federal Emergency Management Agency Director Brock Long said during a news conference Monday that 50 counties in Texas are affected by the flooding and that a tremendous amount of rainfall is in the cards for southwest Louisiana. The rain and floods have been blamed in at least two deaths.

Residents living near the Addicks and Barker reservoirs — that were designed to prevent flooding in downtown Houston — were warned Sunday that a controlled release from both reservoirs would cause additional street flooding that could spill into homes. Rising water levels and continuing rain was putting pressure on the dams that could fail without the release. Harris and Fort Bend county officials advised residents to pack their cars Sunday night and leave in the morning.

As the water rose, the National Weather Service issued another ominous forecast: Before the storm is gone, some parts of Houston and its suburbs could get as much as 50 inches (1.3 meters) of rain. That would be the highest amount ever recorded in Texas.

FEMA’s Long predicted that the aftermath of the storm would require FEMA’s involvement for years.

“This disaster’s going to be a landmark event,” Long said.

The National Weather Service meanwhile warned that the catastrophic flooding would worsen due to heavy rainfall in the coming days and that it would be slow to recede once Harvey finally moves on.

Director Louis Uccellini said during a news conference Monday that up to 20 inches (51 centimeters) of rain could fall in the coming days, on top of the more than 30 inches (76 centimeters) some places have already seen.

Rescuers had to give top priority to life-and-death situations, leaving many affected families to fend for themselves. And several hospitals in the Houston area were evacuated due to the rising waters.

It was not clear how many people were plucked from the floodwaters. Up to 1,200 people had to be rescued in Galveston County alone, said Mark Henry, the county judge.

Houston’s George R. Brown Convention Center was quickly opened as a shelter. It was also used as a shelter for Katrina refugees in 2005.