Thousands of protestors in Bangladesh have crowded into central Dhaka square demanding prime minister Sheikh Hasina's resignation following police crackdown on protestors.

While the authorities had despatched the army to restore order in the wake of protests, it is reported that some former military officers have joined the student movement.

Rallies against civil service job quotas sparked days of mayhem in July that killed more than 200 people in some of the worst unrest of Hasina's 15-year tenure.

Troops briefly restored order but crowds returned to the streets in huge numbers this week in an all-out non-cooperation movement aimed at paralysing the government.

On Saturday, when hundreds of thousands of protesters marched in Dhaka, the police were largely bystanders watching the rallies.

The protests have grown into a wider anti-government movement across the South Asian nation of some 170 million people.

The mass movement includes people from all strata of Bangladesh society, including film stars, musicians and singers, and rap songs calling for people's support have spread widely on social media.