(CNN) A 3-year-old girl is dead and a 4-year-old is hospitalized after their flotation devices slipped off and they went underwater at a pool party in Florida, authorities said.

Harmony Williams was playing in the water at a Tampa apartment complex when she drowned. Witnesses pulled her out and tried to give her CPR, but she was pronounced dead at a local hospital, the Hillsborough County Sheriff's Office said in a statement Tuesday.

Giaonna Chavalier was also rescued and taken to the same hospital, where she is no longer listed in critical condition.

"She is alert, breathing and expected to make a full recovery," police said.

The tragedy happened shortly after 5 p.m. Saturday as a family was hosting a pool party in the apartment pool area attended by about 10 children and three adults.

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