Around 30 people marched in silence through the centre of the city, before uniformed and plain clothed security agents moved in and forced them to disperse, dragging some demonstrators away onto a bus, an AFP reporter saw.

The protest was to support Dung's proposal for a new law on demonstrations, which he said was necessary after a series of rallies earlier this year over a territorial spat with China exposed gaps in existing legislation.

Protests are rare in authoritarian Vietnam, but analysts said some of the anti-China rallies were tolerated because they helped express Hanoi's displeasure with Beijing. Other marches were broken up by police.

"We do not have a demonstration law so it's difficult for the people and for the administration," Dung told the communist country's National Assembly on Friday.

Bloggers immediately rallied around Dung's proposal, and called for the demonstration Sunday to show their support for the move.

The prime minister called for new legislation on protests "to ensure people's rights to freedom and democracy under the constitution and law." Vietnam's constitution allows for the right to demonstrate.

But the proposed law should also focus on "preventing acts and behaviours that undermine social order and security," Dung said.

The law is being drafted by the Ministry of Public Security, local media have reported.

The ministry's police and internal security agents have detained dozens of peaceful political critics who were later sentenced to long prison terms under a crackdown since late 2009, according to Amnesty International.

Protests are still rare in authoritarian Vietnam but have occurred more frequently in Hanoi this year.

For 11 weeks from June, protesters demonstrated against Chinese actions in the South China Sea, the scene of long-standing tensions between the neighbouring countries over rival territorial claims.

Earlier in November, police peacefully dispersed a march of about 150 Vietnamese Catholics protesting an alleged grab of church land by authorities.

Small protests are also often staged by aggrieved landowners outside government offices in Hanoi, alleging they have been given inadequate compensation for land taken by the state for development.

Agence France Presse - November 27, 2011