BANGKOK, Oct 7, 2008 (AFP) - Protesters cut the power to Thailand's parliament building on Tuesday, after police fired tear gas in an attempt to disperse them.

Emergency generators quickly kicked in after a short black-out in the assembly room and Senate building, an AFP reporter at the scene said.

About 1,000 police fired tear gas in an attempt to disperse thousands of protesters massing outside parliament, critically injuring at least three people and hurting dozens more, police and doctors said.

Anti-government protesters from the People's Alliance for Democracy (PAD) marched to parliament late Monday, mobilising against plans to amend the country's constitution, which they say is aimed at helping ousted premier Thaksin Shinawatra.

Police made way for MPs as they arrived at parliament on Tuesday ahead of the new government's first policy announcement.

The PAD began their campaign in late May seeking to force the elected government to resign, raising tensions in the kingdom after they besieged government offices late August.