'Massive' search on for children swept away by Pennsylvania floods

Pennsylvania rescue crews are looking for two children who are missing 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 boy and his two-year-old sister.

The family from South Carolina were on their way to a barbecue when their car was swept away.

The children's father, a four-year-old boy and their grandmother survived.

The identities of the four other people killed in Saturday's flooding is unclear. The victims have not yet been named.

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.

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.