(CNN) Two men were attacked by sharks off the eastern coast of Florida.

The incidents occurred within an hour of one another, 100 miles apart.

The first attack took place around 3:30 p.m. ET Saturday near Jacksonville Beach Pier, according to a witness. RJ Berger said he and his friend Frank O'Rourke were surfing together when a shark knocked O'Rourke off of his board and into the water.

The four-foot shark then bit O'Rourke on the arm, Berger said.

Professional surfer Frank O'Rourke shows off the bite mark on his arm.

The two men managed to catch waves back to shore, where a lifeguard treated O'Rourke for his injuries.

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