Boats sailed through the streets of a Serbian town on Friday on a mission to rescue people trapped by rising waters as the worst floods ever recorded swept Serbia and Bosnia. Some residents of Obrenovac, 30 km (20 miles) southwest of the capital Belgrade, were stranded on the roofs of their homes, calling for help. Prime Minister Aleksandar Vucic said all 25,000 citizens would have to be evacuated. At least five people have died in the unfolding disaster this week. Thousands have been evacuated from homes in central and western areas of Serbia and in neighbouring Bosnia. Around 135,000 households were without power across Serbia and the government approved emergency electricity imports. Another 65,000 were without electricity in Bosnia. "This is a catastrophe.