Pennsylvania rescue crews are searching for two missing children after flash flooding killed their mother and four others over the weekend.

The race-against-time search continued on Monday in suburban Philadelphia for the nine-month-old Conrad Sheils and his two-year-old sister, Matilda.

Their mother, 32-year-old Katie Seley, was killed in the flood, police said.

The South Carolina family were driving to a barbecue when their car was swept away.

Their father, a four-year-old boy and their grandmother survived the floods.

A statement released on behalf of the family said: “Their loving father, Jim Sheils, and their entire family would like to thank everyone for their prayers and support.”

Scott Ellis, brother-in-law to Mr Sheils, read a statement from the family at a press conference on Monday.

“Our family would like to extend our deepest gratitude for the enormous efforts of so many emergency personnel who have been working tirelessly in dangerous and difficult conditions to rescue the victims of this horrific tragedy,” he said.

Upper Makefield Fire Chief Tim Brewer told a news conference on Monday that more than 100 crew members and drones would scour the area for the missing children in a “massive undertaking”.

He said: “As they tried to escape the fierce flood waters, dad took his four-year-old son while the mother and grandmother grabbed the two additional children, ages nine months and two years.

“Miraculously, dad and his son got out safely, however, the grandmother, the mother and the two children were swept away by the flood waters. And we have recovered the mother and she is one of the deceased.”

The grandmother was rescued and treated for injuries at a local hospital.

Along with Ms Seley, four other people were killed in Saturday’s flooding.

Officials confirmed the identities of the other victims as 53-year-old Susan Barnhart, Yuko Love, 64, Enzo Depiero, 78, and 74-year-old Linda Depiero.

The Bucks County coroner confirmed they all died by drowning.

Nearly a dozen cars were trapped by flash floods on Saturday afternoon as Houghs Creek swelled into a fast-moving river.

Three cars were swept away and all the other deceased were found outside their cars, having left their vehicles in an attempt to escape the floods, reports the Philadelphia Inquirer.

By Monday, the waters had receded, revealing roads buckled by the flooding.

Bucks County resident Nick Primola told Reuters he’s grown accustomed to “crazy weather these days”, but his town has never seen anything like this.

According to the National Weather service, much of the northeastern United States will remain under a flood watch until Tuesday evening.

New Jersey Gov Phil Murphy toured the storm-damaged town of Belvidere Monday, where torrential rains caused a landslide that buried a car in mud and rubble. The governor said he has declared a state of emergency to help get FEMA assistance to those who need it most.