A determined search is ongoing for 2 younger siblings who have been swept away with their mom and grandmother throughout flash flooding close to the US metropolis of Philadelphia.

The two kids, a nine-month-old boy and his two-year-old sister, have been in a automotive with each of their mother and father, their brother and their grandmother, when a creek in Bucks County, Pennsylvania, burst its banks.

The father and the four-year-old son "miraculously" managed to flee the flood water.

But the mom, the grandmother, and the 2 younger kids have been swept away alongside the creek.

The mom was later discovered lifeless - certainly one of 5 individuals killed within the flooding - whereas the grandmother survived.

A 100-strong search crew and quite a few drones are on the lookout for the siblings alongside the creek - which drains into the Delaware River.

The fireplace chief of Upper Makefield Township, Tim Brewer, stated the search effort could be a "massive undertaking".

The household are all from Charleston, South Carolina, and have been visiting relations and buddies after they received caught in a flash flood on Saturday, Mr Brewer stated.

"As they tried to escape the fierce floodwaters, dad took his four-year-old son while the mother and the grandmother grabbed the two additional children," the hearth chief stated.

"However, the grandmother, the mother, and the two children were swept away by the floodwaters," Mr Brewer added.

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Flash flooding additionally hit components of New Hampshire, Massachusetts, Connecticut, New York and New Jersey over the weekend.

The governor of New Jersey, Phil Murphy, declared a state of emergency on Sunday. He plans to tour broken areas within the state.

A twister touched down on Sunday morning in North Brookfield, Massachusetts, however no accidents have been reported.

In New Hampshire, a Nascar race on the New Hampshire Motor Speedway was postponed on Sunday because of the flooding.

There have been additionally delays and cancellations at airports within the New York City space over the weekend.