The police say the uncle disapproved of the relationship, and shot at the young man several times in the street. He ran after his victim, stabbing him several times before driving off in his car.
The fight happened at a crossing on the outskirts of the town, where police proceeded to block one of the roads.
The victim was able to give police information on the identity of his attacker before being taken to hospital, where he underwent an emergency operation.
The attacker is still on the loose and apparently armed with a gun and a knife. Police have launched a major hunt for him and are using a helicopter in the search.