Prisoners used "improvised weapons" during clashes on Saturday
Fifteen of the protesters are being force fed, and three of them are being observed in hospital.
Human rights groups say prisoners are frustrated with the military's failure to decide their future.
The US is currently holding 166 men at the facility, most without charge.
Hunger strikes are frequent at Guantanamo, but the current protest - which began in February - is reportedly one of the longest and most widespread.
Guantanamo officials deny claims that the strike began after copies of the Koran were mishandled during searches of prisoners' cells.
Violence erupted at the prison on Saturday as the authorities moved inmates out of communal cellblocks where they had covered surveillance cameras and windows.
Some prisoners used "improvised weapons" and were met with "less-than-lethal rounds", a military spokesman said, but no serious injuries were reported.
Nearly 100 of the detainees have been reportedly cleared for release but remain at the facility because of restrictions imposed by Congress and also concerns of possible mistreatment if they are sent back to their home countries.
The military detention centre opened in 2002 to hold suspects captured in counter-terrorism operations after the 11 September 2001 attacks in the US.
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