Police and fire services were at the scene on Sunday night and the City of Florida said on X that six patients "were declared as trauma alerts," with two of those, who were more seriously wounded, being transported by helicopter.
There was a report of one death, and Clearwater said everyone had been accounted for after the incident.
"All of the injuries are from the ferry. The boat that struck the ferry fled the scene," Clearwater Police Department said on social media.
"The crash involved the Clearwater Ferry, which had more than 40 people on board," police said, adding nearby hospitals were alerted and that the US Coast Guard will handle the probe into the incident.
An NBC News affiliate cited an alert from the city of Clearwater saying the crash happened late at night just west of the bridge.
"The ferry came to rest on a sandbar just south of the Memorial Causeway bridge. All patients and passengers have been removed," police said.
It was the end of the 17-day Sugar Sand Festival on Sunday night and many people were taking the ferry back and forth for the festival, media reports said.
An ABC News affiliate cited Clearwater Mayor Bruce Rector to be saying that the boat that collided with the ferry was privately owned.
"We're working (on) a boat crash off the Memorial Causeway bridge that has resulted in multiple injuries. It's been declared a mass casualty incident by the fire department due to the number of injuries," Clearwater Police Department said in its initial statement.
