WASHINGTON CROSSING, Pa. (AP) — A broad effort to find two young siblings who were swept away from their car during flash flooding in the Philadelphia suburbs over the weekend may soon pivot to underwater searching, authorities said Tuesday.

Upper Makefield Fire Chief Tim Brewer provided an update near the search area, saying the team was still looking for Matilda Sheils, 2, and her 9-month-old brother Conrad Sheils. If the children are not located by day’s end, Brewer said, the focus will be on the water, using dive teams.

With the search in a fourth day, officials acknowledged the many that have asked to volunteer to help but said they are not needed. Brewer asked people to avoid the area.

Some 100 officials, as well as drones and cadaver dogs, have combed the area near the creek that drains into the Delaware River. The search has covered about 117 acres (47 hectares), with those on land logging some 160 miles (257 kilometers), often going back and forth over the same ground, he said.

The children are members of a Charleston, South Carolina, family that was visiting relatives and friends when they got hit by a “wall of water” Saturday, Brewer said.

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, Brewer said. Sheils and his son made it to safety, but Seley and the grandmother were swept away. The grandmother survived, but Seley was among the five people who drowned, according to the Bucks County Coroner's office.

The others who died were 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 deaths and the search for the children have led to an outpouring of support, particularly in social media posts in the suburb about 35 miles (56 kilometers) north of Philadelphia. A community vigil for those affected was planned for Thursday evening.