Online Desk : Thirteen people have died in Kerr County in the US state of Texas, according to authorities, after severe weather and flooding hit parts of the state, reports BBC.

More people are unaccounted for, including at a summer camp where Texas Lieutenant Governor Dan Patrick confirmed around 20 children are missing.

"Within 45 minutes, the Guadalupe River rose 26 feet and it was a destructive flood - taking property and sadly lives," he said in a news conference on Friday.

He read out a statement from all-girls Camp Mystic, where about 700 children were attending, saying there had been a "catastrophic level" of flooding, and informed parents that if they have not been contacted, their child is accounted for.

"That does not mean [the missing children] have been lost. They could be out of communication," the lieutenant governor, who is acting governor while Governor Greg Abbott is on vacation, added.

On Friday morning, flash flooding in the state prompted disaster declarations for the Hill Country and Concho Valley regions.

In Kerr County, the sheriff`s office has reported severe flooding with several people missing and confirmed loss of life.

Rescues and evacuations have been under way since the early morning and there are warnings of more potential flash flooding to come in the state.

The state received several months worth of precipitation in a few hours, according to officials, leading to dangerous flash floods.

Governor Greg Abbott said Texas was providing "all necessary resources to Kerrville, Ingram, Hunt and the entire Texas Hill Country dealing with these devastating floods".

The region is to the north-west of the city of San Antonio.

Pictures show the deep flood waters swamping bridges and fast moving water swirling down roads.

"Folks, please don`t take chances. Stay alert, follow local emergency warnings, and do not drive through flooded roads," Texas Department of Agriculture Commissioner Sid Miller said.

The Kerr County Sheriff`s Office told residents near creeks, streams and the Guadalupe River to move to higher ground.

Kerrville Mayor Joe Herring said there was no indication the floods were going to be so devastating as the country does not have an early warning system in place, as reported by The Kerrville Daily Times.

Separately, in New Jersey, authorities say at least three people died in the state following heavy rain and thunderstorms on Thursday night.

Among the three killed were two men, aged 79 and 25, who died after a tree fell onto their car in Plainfield during Thursday`s severe storm.

A 44-year-old woman was also killed when a tree fell on her vehicle in North Plainfield.

"Our hearts are heavy today," said Mayor Adrian Mapp of Plainfield. "This tragedy is a sobering reminder of the power of nature and the fragility of life."