Parts of southern Texas are facing a rare and dangerous flood threat as slow-moving storms continue to bring heavy rain across the region. Weather officials have issued a Level 4 of 4 high risk for flash flooding, warning that some areas could experience catastrophic impacts.

The highest risk covers the western Hill Country, the Edwards Plateau, and the Rio Grande Valley near the US-Mexico border. The Weather Prediction Center said significant flash flooding is expected to continue through Tuesday and into early Wednesday as more rounds of rain move across the area.

Many communities had already received between 6 and 12 inches of rain before Tuesday morning. Forecasters say some locations could receive another 10 inches or more before the rain begins to ease. Additional showers and thunderstorms are also expected through the end of the week, increasing the risk of flooding.

Officials warned that roads, homes, and low-lying areas could quickly become flooded. Creeks, rivers, and streams are also expected to rise, with some likely to overflow their banks. Moderate to major river flooding remains possible in several locations.

Flood watches are in effect for more than six million people across central and southwest Texas. Cities under the watch include Austin, San Antonio, Del Rio, and San Angelo. Areas farther east, including Houston, could also experience localized flooding.

Emergency crews have already carried out several water rescues after vehicles became trapped in floodwaters. In Medina County, about 18 roads became impassable, and one bridge was submerged. Another water rescue took place near Sabinal in Uvalde County.

Texas Governor Greg Abbott activated the state’s emergency response ahead of the storms. Water rescue teams, helicopters, and other resources have been deployed to help communities affected by flooding. Officials continue to urge residents not to drive or walk through flooded roads, as water levels can rise quickly and become extremely dangerous.

The flood threat comes just over a year after deadly flooding struck the Texas Hill Country, claiming more than 130 lives. The region is especially vulnerable because its rocky landscape and shallow soils prevent heavy rainfall from soaking into the ground.

Forecasters expect the flood risk to remain high through Thursday before gradually easing later in the week. However, isolated showers and thunderstorms could continue into Friday and Saturday, especially across western parts of the state.