By Gul Yousafzai

ISLAMABAD (Reuters) - A blast targeting a police van killed more than 20 people in Pakistan's northwestern city of Quetta on Wednesday, a hospital spokesman said, as the South Asian nation goes to the vote to choose a new government.

The blast happened near a polling station, said a Reuters witness in Quetta, capital of Pakistan's province of Baluchistan, but it was unclear if voting had been disrupted.

"Over 20 bodies and 28 injured have been shifted to civil hospitals," Dr Waseem Baig, a spokesman for a Quetta hospital, told Reuters.

Television images showed a charred police vehicle, cordoned off by security officials.

Samaa TV, which put the death toll at 20, said a "suicide attacker" was responsible for the attack. Rival Geo TV said 22 people had been killed.

(Additional reporting by Idrees Ali; Writing by Drazen Jorgic; Editing by Clarence Fernandez)