Islamabad : By-elections on 21 vacant seats of National and Provincial Assemblies will be held on Sunday.In a statement of Election Commission of Pakistan, polling will be held on five National Assembly seats, twelve Punjab Assembly seats, two seats of Khyber Pakhtunkhwa Assembly and two seats of Balochistan Assembly.Polling will start at 8:00 in the morning and it will continue till 5:00 pm without any break.