The Metropolitan Police Bureau will deploy four companies of police to maintain peace and order at the Democracy Monument in central Bangkok where pro-democracy "Red-shirt" supporters are scheduled to hold a mass rally to celebrate the 1932 Revolution on Sunday, local media reported on Saturday.

Police will be deployed in areas nearby the monument and two intersections nearby, said Pol Maj Gen Wallop Prathummuang, commander of Metropolitan Police Division 6, on Saturday.

Police expected about 50,000 red-shirts to turn out to join the planned mass gathering.

Red-shirt leader Thida Thavornsate said their protest on Sunday has two purposes. One is to commemorate the end of the absolute monarchy in Thailand 80 years ago, and the other is to show their opposition towards any intervention in the democratic process.

The revolution was a nearly bloodless transition on June 24, 1932, in which the system of government in Thailand was changed from an absolute monarchy to a constitutional monarchy.

Thida said the mass gathering of red-shirts would begin about noon on Sunday and will end about midnight, according to the Bangkok Post online.