BUDAPEST - Plummeting river levels have already brought shipping to a standstill in parts of Serbia, squeezing fuel imports and energy production -- and now heatwave warnings have been issued in the Balkans. Serbian forecasters said a long-term heatwave had begun, with temperatures expected to reach around 40C in some places on Friday, and the intense heat could last for close to a fortnight. Similar warnings were also issued across the region, and the authorities braced for an increase in wildfires as rising temperatures coupled with drought conditions. The warning comes as successive heatwaves hit Europe, driving deadly wildfires amid a major drought -- conditions scientists say have been worsened by human-induced climate change. Along the Serbian stretch of the Danube, a lack of rainfall has left vessels stranded and exposed sandbanks, with some parts now shallow enough to cross on foot.