Six family members are believed to have been killed when their van was swept away by floodwaters as they tried to flee Tropical Storm Harvey.

The van became submerged by high water Sunday after crossing a bridge in Greens Bayou, Texas.

Four children — between the ages of 6 and 16 — and their great-grandparents tried to escape through the vehicle’s back door but couldn’t get out of the van before it went under water, relatives told KHOU-TV.

The driver, who is the children’s great-uncle, scrambled out of the car before it was submerged and clung to a tree.

Houston Police Chief Art Acevedo couldn’t confirm the deaths but told The Associated Press that he’s “really worried about how many bodies we’re going to find.”

Texas Gov. Greg Abbott on Monday afternoon said flooding from the devastating storm has caused “one of the largest disasters America has ever faced.”