POLICE shot dead six Opposition party supporters in India's southern Andhra Pradesh state overnight, sparking a riot in which hundreds of political activists stoned to death a policeman and burned cars and trucks.

At least two dozen police officers were injured, along with more than a dozen supporters of the Opposition Telugu Desam Party (TDP), police said.

The trouble started when police in Penukonda, 410km south of the state capital Hyderabad, barred Opposition activists from an administration office where a TDP candidate was filing nomination papers for a state by-election.

TDP workers hurled stones and bottles at police, beating up some of them, and attacked nearby shops.

Police responded by opening fire, killing six TDP supporters, police said.

Deputy Inspector General of Police N Jayarami Reddy said the mob had gone "berserk".

Every year, political violence claims dozens of lives in Andhra Pradesh, whose ruling Congress Party also heads the federal Coalition.

On January 26, unidentified gunmen killed the sitting TDP lawmaker from Penukonda, resulting in the need for a by-election and heightening political tension.

The TDP blamed the ruling Congress for the latest violence.

"The Congress party wants to convert Andhra Pradesh into a graveyard," TDP president N Chandrababu Naidu told a news conference in Hyderabad.