WASHINGTON CROSSING - Pennsylvania authorities drew on 100 people, drones and cadaver dogs Monday in their search for two missing children whose family’s car was swept away in flash flooding that ravaged the East Coast over the weekend. Other parts of the country endured threateningly high temperatures and severe air pollution from Canadian wildfires.

In eastern Pennsylvania, authorities described Monday’s search for missing Matilda Sheils, 2, and her 9-month-old brother Conrad Sheils as a “massive undertaking” along a creek that drains into the Delaware River. The children are members of a Charleston, South Carolina, family that was visiting relatives and friends when they got caught in a flash flood Saturday.

The children’s father, Jim Sheils, grabbed their 4-year-old son, while the children’s mother, Katie Seley, and a grandmother grabbed the other children, said Upper Makefield Township Fire Chief Tim Brewer. Sheils and his son made it to safety, but Seley and the grandmother were swept away.

The grandmother survived, but Seley, 32, was among five killed by the floods.

“A wall of water came to them; they did not go into the water,” Brewer said of the Sheils family.

Scott Ellis, an uncle to the missing children, described the family as “utterly devastated.”

Monsignor Michael Picard of St. Andrew Roman Catholic Church, where family members are parishioners, said he spoke with the grandparents Sunday.

“No matter how long I’ve been doing this - over and over and over, many, many years - you find yourself still helpless and without words to make people feel more comfortable,” Picard said. “And so you just simply pray with them for a few minutes.”

Pennsylvania’s flash floods also drowned Enzo Depiero, 78, and Linda Depiero, 74, of Newtown; Yuko Love, 64, of Newtown; and Susan Barnhart, 53, of Titusville, New Jersey, Bucks County Coroner Meredith Buck said.

The county commissioners signed an emergency declaration in response to the flooding.

Other parts of the saturated Northeast began drying out Monday after drenching weekend rains resulted in flash flooding in parts of New Hampshire, Massachusetts, Connecticut, New York and New Jersey. New Jersey Gov. Phil Murphy declared a state of emergency Sunday.

The Vermont Emergency Management agency reported that swift-water rescue teams conducted an additional six rescues overnight. The agency also was monitoring areas at risk for landslides.

U.S. Transportation Secretary Pete Buttigieg and Vermont Gov. Phil Scott toured some of the destruction from recent torrential rains on Monday, including a damaged inn that was cut in half by floodwaters.

Buttigieg said Vermont has endured two storms that would be called “once-in-a-century” events in the span of just 12 years.

“We can’t go into the future requiring communities to put everything back exactly the way it was if a 100-year flood is about to become an annual event,” he said.

More rain was forecast for today.

Sunday’s storms led to hundreds of flight cancellations at airports in the New York City area, and hundreds more flights were delayed.

New York Gov. Kathy Hochul said 5 inches of rain fell within two hours in Suffolk County on Long Island. The state saw $50 million in damages from storms in the past week.

In North Carolina, floodwaters were blamed for the death of a 49-year-old woman whose car was swept off a road in Alexander County late Saturday. A man who was in the car with her was rescued.

Meanwhile, extensive swaths of the northern United States awoke to unhealthy air quality Monday morning or were experiencing it by midafternoon, according to the Environmental Protect Agency’s AirNow.gov Smoke and Fire map.

Fine particle pollution caused by smoke from Canada’s wildfires is causing a red zone air quality index, meaning it is unhealthy for everyone. The particles are tiny enough to get deep into the lungs and cause short-term problems like coughing and itchy eyes, and in the long run, can affect the lungs and heart.

On Monday afternoon, cities and regions hitting that mark included Lincoln, Nebraska; Peoria, Illinois; Fort Wayne, Indiana; Cleveland and Columbus in Ohio; Huntsville, Alabama; Knoxville and Chattanooga in Tennessee; Greensboro, North Carolina; Pittsburgh, Pennsylvania; and Syracuse and Utica in New York.

Sensitive groups, including people with heart and lung disease, older adults, children and pregnant women, should consider staying inside, advisories warn.

Elsewhere in the U.S., thousands of people in Kansas and Missouri were without power from weekend storms that swept those states. Kansas’ largest electric power provider, Evergy, said it could take days to restore service to all customers. The timeline could create difficult conditions for some people as more storms and stifling heat were expected in Kansas and Missouri early this week, according to the National Weather Service.

In the West, a mountain biker died Saturday in blistering desert heat east of San Diego after he and three fellow bikers helped rescue four hikers who were without water.