A 9-year-old boy in Kentucky was swept away by floodwaters on Friday, one of at least 16 people to die in a series of dramatic storms that continue to pummel the US.

High winds and heavy rain continued to batter states including Arkansas, Tennessee and Kentucky on Saturday, delaying recovery efforts.

Forecasters at the National Weather Service said to expect "potentially historic" rainfall and wide temperature swings from the central US to the East Coast into Sunday.

The boy was reportedly walking to his school bus stop on Friday morning when he was overtaken by flooding. The Frankfort Police Department, in Frankfort, Kentucky, confirmed it recovered his body about two hours later.

"We are deeply saddened at this horrific tragedy that claimed the life of one of our students," Franklin County Schools Superintendent Mark Kopp said at a news conference on Friday.

Kentucky Governor Andy Beshear called the boy's death an "unimaginable loss". He also confirmed another death - that of an adult - in Kentucky on Saturday.

"We need everyone to understand that all water poses a risk right now. Let's do everything possible to keep our loved ones safe," he said in a statement.

National Weather Service forecasters said severe thunderstorms and flash flooding were expected across a wide band of the central US that extended from Arkansas and Louisiana to Western Pennsylvania into Sunday before the system would weaken and move to the East Coast.

As of Saturday afternoon, more than 162,000 people were already without power in Arkansas, Texas, Missouri and Oklahoma. Mississippi, Tennessee and Kentucky had already declared states of emergency earlier in the week.

Forecasters said the storms Saturday had "the makings of a catastrophic, potentially historic heavy rainfall and flash flood event, with some locations potentially seeing rainfall amounts as high as 10-20 (inches) when all is said and done".

Even when the rain stops, swollen rivers will continue to pose a danger, forecasters said. Changes in pressure and high winds also puts the area from eastern Texas to western Tennessee at enhanced risk for tornados.

It has been a punishing week of weather for the region. Dozens of tornados have been reported and hundreds of counties have spent days under storm warnings since Wednesday.

Tennessee has seen 10 deaths, according to CBS, the BBC's American news partner. Other deaths have included a man and his teenaged daughter in Tennessee and a 68-year-old man in Missouri who reportedly stopped to help a stranded driver.

The same region was hit by tornadoes, wildfires and dust storms that killed 40 and left "staggering" damage in March.