The pair was dragged to safety by Coast Guard Jonathan Rivera and his friend Jimmy Vega, and the two rescuers have now spoken out about the incident.
Rivera claims they were called over to the scene by a man and a woman on another jet ski, who were struggling to keep heavyset Kingston afloat as his life jacket had slipped off.
After diving into the water, Rivera noticed the singer was "puking up blood out of his mouth", adding, "(He was) convulsing and throwing up blood all over me."
A police boat arrived soon afterwards and Rivera tells TMZ.com Kingston was able to mutter the words, "I'm going to be OK."
And Vega admits Kingston and his friend were lucky to have been rescued when they were.
He says, "We were about to turn back around (and go home) when we noticed him. I truly believe if we did turn around, he would not be with us today."
Kingston, who is not thought to have suffered a head injury, was initially said to be in a critical condition as he underwent treatment in the trauma ward, but was subsequently moved to the intensive care unit on Monday (30May11) after showing signs of improvement.
Officials are still investigating the cause of the crash but alcohol is not thought to be involved.