Skies were clear and sunny when a power boat packed with 12 people slammed into a docked tug boat, killing five occupants of the pleasure craft and seriously injuring seven others, authorities and witnesses said Monday.

The 22-foot power boat crashed into the rear of the tug at about 7 p.m. Sunday near Palm Valley in St. Johns County, about 25 miles southeast of Jacksonville, said Florida Fish and Wildlife Conservation Commission spokeswoman Joy Hill. The Intracoastal Waterway runs along Florida's east coastline.

Debi Davis and her husband Herb, who live nearby, watched afterward as rescuers pulled the victims from a narrow section of the waterway.

"You could hear screaming as they pulled one woman out on a gurney board," Davis said.

Six people are recovering at Shands Jacksonville hospital in Jacksonville, authorities said. Two are listed in critical condition, one in serious condition and three are in fair condition.

Visibility was clear when the accident occurred, but Davis said she was surprised by the amount of damage and the death toll.

"I don't know how they could have missed it, the tug is hard to miss," she said.

Davis said that the waterway is usually busy on Sundays.

The victims' names have not been released. Hill said investigators were still trying to verify their identities.

"Investigators are looking at anything that may have caused this," Hill said, including the speed and capacity of the boat, lighting conditions and whether alcohol may have been a factor.

Investigators have been tightlipped about what they have learned.

Chuck Mulligan, a spokesman for the St. Johns County Sheriff's Office, said deputies and paramedics had to scramble to find construction material to build a bridge to the victims on the pier under construction.

"They did this knowing time was critical and once medical treatment was given those patients, they would be need to be brought off the crash site and on the makeshift dock," Mulligan said.