SAN FRANCISCO -- A boat capsized in San Francisco on Saturday afternoon, and all of the 30 people onboard were rescued.

A San Francisco Fire Department spokesperson initially posted a message on social network Twitter that about 30 juveniles were aboard the boat and some were trapped under the hull.

A U.S. Coast Guard rescue crew, including divers, was dispatched to the scene off the historic Pier 45, one of the tourism destinations along the city's waterfront, in the heart of the Fisherman's Wharf neighborhood.

However, confirming that 27 adults and three children were involved, a police spokesman said a five-year-old boy was pulled out water unconscious and was resuscitated before being sent to a hospital in the city in northern California on the U.S. west coast.

An additional five adults and two children were hospitalized with varying degrees of injury.

An ongoing investigation is led by the police on what caused the incident while the boat, reportedly a recreational sailboat named "Khalessi," is submerged.

Amateur video footage shows none of the people in the water appeared to wear life jackets when at least five boats were there to help, suggesting that their vessel turned upside down in a short time.

Fire department spokesman Bob Postel acknowledged that it could be catastrophic without help from bystanders on private boats and efforts by several public safety agencies that sent vessels to rescue those in cold water.

There was an Air Show on Saturday in the skies above the waterfront, where U.S. Navy Blue Angels, a flight demonstration squadron, and U.S. Air Force's F-22 Raptor were featured. The event, part of the annual Fleet Week celebration, usually attract 1 million people around the San Francisco Bay Area.

It was the second incident of the kind in a week. On September 2, 15 children and one adult chaperone were rescued from San Francisco Bay waters after their catamaran flipped over.