South African police say a foreigner was seriously injured when his shop was petrol bombed.

Police spokesman Kay Makhubela said on Friday that the man's shop was attacked by South African small business owners on Thursday night. He said police arrested nine South Africans, who were demanding that the foreigner close his shop and leave the area.

Makhubela said that in a separate incident, police arrested four foreigners for possessing illegal firearms. Makhubela said the immigrant business owners fired shots in the air after they were accosted by another group of local business owners, demanding they close shop.

Both incidents happened in Soweto in Johannesburg, where immigrant-owned shops were looted for several days in January after a Somali shop owner shot and killed a 14-year-old boy.