Protests have erupted in three part of Syria in the gravest unrest in years in one of the Mideast's most repressive states, reports say.

The government's TV channel and news agency said "infiltrators" in the southern town of Deraa caused "chaos and riots" and smashed cars and public and private property before they attacked riot police who chased them off.

It said a similar demonstration in the coastal town of Banyas dispersed without incident.

Amateur video footage posted on YouTube and Twitter showed large groups of protesters in several cities, but its authenticity could not be immediately be independently confirmed.

Serious disturbances in Syria would be a major expansion of the wave of unrest tearing through the Arab world for more than a month in the wake of pro-democracy uprisings that overthrew the autocratic leaders of Tunisia and Egypt.

Syria, a predominantly Sunni country ruled by minority Alawites, has a history of brutally silencing dissent - including a notorious incident in which President Hafez Assad crushed a Muslim fundamentalist uprising in the city of Hama in 1982, killing thousands.