A small boat carrying six people sank in a lake Wednesday, killing two children, authorities said.

Fire officials initially reported that six children and two adults were aboard the boat on Robco Lake in south Memphis near the Mississippi state line, but police later said there were four children and two adults aboard. The first number may have included swimmers from shore attempting to rescue the victims, police said.

The boat overturned and began sinking about 50 yards from shore, authorities said.

An 11-year-old girl was underwater for about 30 minutes before a firefighter pulled her off the bottom of the lake. She and a 10-year-old boy were taken to a hospital, where they were later pronounced dead, police said.

Five other people were taken to the hospital, including a rescuer who swam from shore, authorities said. Their identities and conditions were not released, nor were the identities of the victims.

The passengers were aboard a johnboat, a small wooden or aluminum flat-bottomed boat generally used for fishing on calm waters. Police said the 10- to 12-foot boat is designed to carry only two or three people and was overloaded before it overturned.

Firefighter Ryan Jones said he was swimming in the lake looking for survivors while another rescuer in a boat used a long pole to probe the bottom.

"He felt like he grabbed something. I swam down, felt around and realized I had a girl," Jones told The Commercial Appeal. "We got her up and got her in the boat."

Neighbor Leo Brown said he heard screams from a few doors down.

"I realized that people were in trouble. I saw a girl and she was holding a baby," said Brown, 54, who stripped off his pants and jumped in the water to rescue them. "I couldn't think to do anything but go in."

The relation between the victims was not clear. Witness Claire Christian told WMC-TV in Memphis that she had been spending the holiday with the family of some of the victims.

"They were just on the ride and it just happened so quick," Christian said.