Kingston, 21, suffered a broken jaw, fractured wrist and water in his lungs, according to the sources, who both asked not to be identified since they were not authorized to speak to the media.
A publicist for Epic Records, which distributes his music, issued a statement Tuesday morning saying Kingston was in "critical but stable condition" in the intensive care unit of a Miami hospital.
Kingston had just bought the jet ski days before, as he was moving into a new house in Miami, one source said.
His life vest apparently fell off during the crash, causing Kingston to sink below the water, according to witnesses.
Kingston shot to fame in 2007 when his debut song "Beautiful Girls" became a No. 1 hit in the U.S.