The tornado struck the townships of Jinshan and Fengpo on the island province, cutting off power supply, uprooting trees and ripping roofs off houses, state-run Xinhua news agency reported.
The tornado has affected 749 people in the two towns.
Four of the 11 injured suffered serious injuries.
They are receiving treatment at the People's Hospital of Hainan Province.
A total of 178 homes were damaged in the tornado.