Authorities have warned that power cuts could last for days in Texas, where hundreds of thousands of homes and businesses remain disconnected from the power grid after another night of severe weather.
A teenager died on a construction site on Tuesday when a partly-built house collapsed in a storm.
Texas was among the states earlier battered by deadly storms and tornadoes over the Memorial Day holiday weekend, during which at least 24 people died.
Hail, damaging wind and flash flooding remain possible in the region, and in Kansas and eastern Colorado, forecasters say.
At the same time, "anomalous heat" continues to affect southern parts of the state as well as southern Florida, according to a Wednesday morning update from the National Weather Service (NWS). Temperatures are also expected to climb in the south-west and parts of California.
During the Texan storms, a disaster declaration has been made for Dallas County. There have been accounts of flooded streets, and downed trees and power lines in Dallas city.
Weather-related fires have burned down homes and a historic church in or near the city, and widespread travel disruption has been reported, including hundreds of flight cancellations at Dallas-Fort Worth International Airport.
Local officials have warned that it could take time for power to be restored.
"This unfortunately will be a multi-day power outage situation," Dallas County Judge Clay Jenkins said on Tuesday.
About 500,000 customers in Texas alone are without electricity, according to monitoring site Poweroutage.us - following an earlier peak of more than a million.
The death of a 16-year-old was announced late on Tuesday by the Montgomery County Sheriff’s Office, after a house under construction collapsed during a storm.
Most workers on site were able to safely flee when they noticed the structure begin to shift - apart from the teenager.
Texas earlier suffered a devastating weekend of storms that killed several people in the state, injured more than 100, and damaged or destroyed many homes.
There were other storm-related deaths in Arkansas, Oklahoma, Alabama and Kentucky. In the latter state, the story has emerged of a man whose family home was flattened by tornadoes for the second time in three years.
“This time, everything that we have is gone,” Devin Johnson told ABC News.
The unrelenting harsh weather for parts of the US comes as forecasters warn of a possibly "extraordinary" 2024 Atlantic hurricane season, beginning next month.
Record-high sea surface temperatures are partly to blame, as is a likely shift in regional weather patterns.
While there is no evidence climate change is producing more hurricanes, it is making the most powerful ones more likely, and bringing heavier rainfall.
