Officers at the Khlok Kloi Police Station were notified of the incident by a motorist at 7:40am.
Police arrived to find a black-red BMW motorbike parked just metres short of the exact halfway mark on the bridge, where the division is made between Phuket and Phang Nga province.
As the motorbike had been parked on the Phang Nga side of the line, investigation of the case was handed to Khok Khloi Police to conduct.
The incident marked the second time in 10 days that a person has jumped off one of the bridges at the northern end of Phuket into the fast-moving water below.
Buncha Suksunit, 25, a resident of Baan Pru Sompan in Moo 8, Tambon Thepkrasattri, parked his pickup truck halfway across Thao Srisoonthorn Bridge, leading off the island, and jumped over the side late on Nov 3.
Despite days of searching, his body has yet to be recovered.
The search for the man who jumped into the water today is already underway.