The search for the 9-month-old who was swept away by floodwaters in southeast Pennsylvania has concluded after 12 days of searching, with no sign of the child, authorities said Wednesday.

The baby boy, Conrad Sheils, his 2-year-old sister Matilda "Mattie" Sheils and their mother vanished as the family was trying to escape intense flooding that hit their family's car on July 15, when a violent storm slammed Bucks County, Pennsylvania, authorities said.

Mattie's body was found on Friday in the Delaware River, 32 miles away from where she was swept away. Crews had previously found the body of their mother, 32-year-old Katie Seley.

On Wednesday, local police announced the search for Conrad had ended.

"At this point, we have exhausted all means of attempting to locate Conrad," the Upper Makefield Township Police Department said. "With broken hearts, we regretfully announce that the active search for Conrad has concluded."

Crews for days had conducted a massive search effort involving hundreds of personnel, drones, boats, K9s, divers, sonar and air assets, according to the department.

Marine units have been checking the Delaware River, with K9 teams searching the islands in the river and along its banks, police said.

"Like all of you, we are truly heartbroken and saddened," the police department said. "Although, at this time, we were unable to reunite Conrad with his loving family, he will forever live in our hearts and he will never be forgotten."

The Sheils children and their family were visiting from South Carolina and were driving to a barbecue when the flash flooding hit on July 15 and a "wall of water came to them," Upper Makefield Fire Company Chief Tim Brewer previously said.

In their attempt to escape, the mother and a grandmother grabbed Mattie and Conrad. The father grabbed the children's 4-year-old brother.

The father and the 4-year-old "miraculously" made it to safety, the fire chief said. But the mother, grandmother and younger children were swept away.

The children's grandmother survived and was treated at a hospital, authorities said.

Floods are among the deadliest weather hazards in the US, according to the National Weather Service. It only takes 2 feet of rushing water to carry away most vehicles, including pickups and SUVs, according to the weather service.