Florida's Fish and Wildlife Conservation Commission said Tuesday that Sidney Renea Good of Roanoke and Alexis Fairchild of Huntington "were parasailing in a tandem harness over the Gulf of Mexico off Panama City Beach when an afternoon storm developed with strong winds."
The winds kept the chute aloft despite several attempts to winch the riders back onto the vessel, the commission said.
The anchor was set to keep the boat from being pulled onto shore and then the towline detached, it said, making it impossible for the girls to control the chute.
The two hit power lines, buildings and parked vehicles, the commission said.
Good and Fairchild were transported to Bay Medical-Sacred Heart in Panama City.
According to FWC investigators, the girls remain in critical condition.
#PrayForSidneyAndAlexis is trending locally on Twitter and a GiveForward fund has been set up to raise money to help pay for their care.
Witnesses told The News Herald (http://goo.gl/RNvB2) that the strong winds caught the detached parasail and tossed the teenagers around the beach after the line broke.
Vacationers Cole Adair and Michael Kennedy, both from Georgia, told the newspaper that they tried to help after the parasail smashed into a SUV on the ground.
"It was gruesome," Kennedy said.
Kennedy and Adair said both victims went limp after crashing into the side of The Commodore Condominiums and stayed that way for several seconds before they reached the ground.
"It seemed like a long time," Adair said.
Tourist Amy Barron said she saw the women hit either a power line or a utility pole before they crashed in the parking lot.
"We knew they were going to hit, but there was nothing we could do about it," Barron said.
FWC spokeswoman Karen Parker said investigators are looking into the possibility of an equipment failure. She said the investigation could be lengthy.
The Associated Press contributed to this story.