STONE TOWN, Zanzibar, Oct 18 (Reuters) - Supporters of a separatist Islamist group in Zanzibar looted shops and fought with police on Thursday after their leader disappeared, witnesses said, the third outbreak of violence this year on the Indian Ocean archipelago.

Supporters of Sheikh Farid Hadi, a leader of the Islamic Uamsho (Awakening) movement who has not been seen since Tuesday, threw stones at police and blocked roads with cut-down trees and burning tires in island's main town.

"Police are everywhere and firing teargas. There is nobody around town and the shops are closed. It's a terrible situation," Said Salleh, 40, a businessman from Zanzibar, told Reuters over the phone.

Witnesses said protesters looted shops and video footage showed a number of rioters holding machetes and hiding their faces with balaclavas.

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