A Kansas doctor who fought off a 12-foot tiger shark last week in Hawaii described seeing a "dark gray cloud" in the water that kept getting bigger seconds before the fearsome fish ripped into him.

"I just saw a dark gray cloud and I didn't know what it was," 58-year-old Ken Grasing told KCTV. "The cloud was getting bigger, and eventually I could see it was a shark. I said, 'Oh no! This is a shark. This is a shark attack.'"

Grasing, a physician from Overland Park, Kansas, was snorkeling Wednesday with his family in 4 feet of water in Hapuna Bay off the Big Island when the massive shark attacked him, according to media reports.

Grasing suffered deep cuts to his left forearm and a gash on his left thigh, according to the station. He reportedly struck the shark in the head with his right hand as it circled around him -- saying it felt like hitting a wall. 

Grasing, who said he didn't feel pain after the bite, was flown to a hospital where he underwent surgery to repair nine tendons, one nerve and a muscle.

"It happened within seconds," he told the station. "The shark was moving so quickly toward me that I didn't realize it was going to bite me until I saw my arm was just mangled ... I was yelling for help and eventually a very brave man came and took me and pulled me out of the water."

Grasing, who was vacationing with his family, said he feared for his two sons who were standing near him. He was back home in Kansas Monday and said he's expected to regain use of his arm after intense rehabilitation, KCTV reported.

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