The body of a young girl found along a river in Pennsylvania is believed to be one of two missing children swept away by flash floods last weekend.

Officials believe the body is of two-year-old Matilda Sheils, who was reported missing with her nine-month-old brother Conrad.

Their mother, 32-year-old Katie Seley, was killed in the flood, police said.

The South Carolina family were driving to a barbecue when their car was swept away.

Their father, a four-year-old boy and their grandmother survived the floods.

The body was found near a Philadelphia wastewater treatment plant about 30 miles (50 km) from where Matilda was swept away, officials told a news conference.

Based on the description and clothing found on the child’s body, officials believe it to be that of Matilda. A full autopsy will take place on Saturday.

The search for Conrad will continue.

The children’s disappearance sparked an enormous search. 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”.

The family was visiting relatives when they were reportedly hit by a “wall of water”, officials said.

Four other people were killed in last Saturday’s flooding.

Officials confirmed the identities of the other victims as 53-year-old Susan Barnhart, Yuko Love, 64, Enzo Depiero, 78, and 74-year-old Linda Depiero.

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, the Philadelphia Inquirer reported.