Chinese police have shot dead four people who allegedly attacked a Communist Party office in the restive Xinjiang region on Wednesday, state media said, in the bloodiest such incident in months.

The four "rioters" drove up to a local party office in Moyu County and "detonated (an) explosive device", killing one person and injuring three others, the official Xinhua news agency reported, citing a statement from the local authorities.

The four assailants were then "shot dead by police", Xinhua added, without specifying whether they were killed on the spot or later in the day.