KARACHI Two people were wounded in a bomb blast in the tense Pakistani city of Karachi on Wednesday after a night of violence in which two people were shot dead and dozens of buses were torched ahead of a city-wide strike.

"A small bomb was placed under a parked car and that car was totally destroyed," said a policeman at the scene.

Police and paramilitary units were out in force on the streets of the city, supported by army patrols.

Most shops and businesses were shuttered, roads were largely deserted and there was little public transport, Reuters said.

The strike was called to protest against alleged police brutality on Sunday during demonstrations against shortages of irrigation water in Sindh Province.

"We shifted two dead bodies to the hospital in our ambulances," said a worker from the Edhi Charity Ambulance Service. Police said at least 13 buses were set alight overnight.

The strike was called by the Muttahida Qaumi Movement (MQM) and Jiye Sindh Qaumi Mahaz (JSQM).

The MQM, mainly comprising Urdu-speaking Muslim immigrants from India, together with the nationalist JSQM which represents Sindhis, the traditional inhabitants of Sindh Province, are demanding greater autonomy for Pakistan's four provinces.

The groups last called a province-wide stoppage against the water shortages in mid-April when Karachi, the capital of Sindh Province, and other major cities were brought to a standstill.