An Oklahoma man died after he was swept away by flooding Wednesday as heavy rain struck the state and Texas, where around 16 million people were under high water alerts, officials said.

The man in Pottawatomie County died after his vehicle was swept off a roadway around 12:30 p.m., and after a sheriff’s deputy who tried to save him also became trapped in the water, the sheriff’s office said. The deputy was rescued by firefighters.

“Tragically, despite every effort made, the individual in distress could not be reached in time and passed away at the scene,” the sheriff’s office said in a statement on social media. “Our hearts are heavy tonight for this loss of life, and we extend our deepest condolences to the man’s family and loved ones.”

The death occurred as roadways and other areas in Oklahoma and the Dallas area flooded due to heavy rainfall caused by a stalled frontal boundary, the National Weather Service said.

The heavy rainfall there came a day after severe weather contributed to the deaths of four people in Pennsylvania, one of whom was electrocuted as he tried to extinguish a mulch fire, police there said.

Around 2 inches of rain in Wichita Falls, Texas, and 2.8 inches in Lawton, Oklahoma, forecasters at the weather service in Norman, Oklahoma, said.

Around 16 million people were under flood watches or warnings in Oklahoma, Texas and Missouri on Wednesday afternoon, according to the weather service.

Tornado watches also covered an area where almost 5 million people live, from eastern Texas to northern Louisiana and most of Arkansas Wednesday afternoon, it said.

The heaviest rain threat was for southeastern Oklahoma, into northeastern Texas and western Arkansas, the weather service said.

The heaviest rain had moved out southeastern Oklahoma by late Wednesday afternoon, the weather service in Norman said, but rivers were expected to continue to flood through Thursday.

In the Dallas area, a flood warning remained in place for the Rowlett Creek Near Sachse until 7:50 a.m. Thursday. Moderate flooding was expected, the weather service said.

The rainfall for the south-central United States is expected to end Thursday, but the risk of thunderstorms will then move to the Mississippi, Ohio, and Tennessee valleys, the weather service said.