* More than 20 confirmed dead in Bosnia, Serbia
* Heaviest rainfall in over a century
* River levels still rising
By Matt Robinson
BELGRADE, May 18 (Reuters) - Two Russian cargo planes carrying food, generators and rescue boats landed in Serbia on Sunday as part of a relief effort after the worst floods in over a century killed more than 20 people in the Balkan country and neighbouring Bosnia.
River levels were still rising in the Serbian capital Belgrade and west towards the Bosnian border, threatening power stations where volunteers joined the army and emergency services in building sandbag barriers.
Tens of thousands of homes were without electricity in Serbia and around 150,000 in Bosnia, where whole swathes of the northeast of the country were under water.
In the worst-hit Serbian town of Obrenovac, waters receded overnight, easing rescue efforts. Authorities say there are fatalities after huge parts of the town, about 30 km (18 miles) southwest of Belgrade, were submerged under water.
"I carried my kids out on my back, then waited 12 hours to be rescued myself," said 40-year-old Obrenovac resident Dragan Todorovic, who spent the night in a Belgrade sports hall with dozens of other families. "The house was new, built two years ago for 100,000 euros. What now?"
Three people were confirmed dead in Serbia by Friday, following days of the heaviest rainfall since records began almost 120 years ago.
In Bosnia, the death toll reached 19 on Saturday, with nine bodies recovered from the northeastern town of Doboj after what the regional police chief described as a "tsunami" of water 3-4 metres high.
Rescue teams and humanitarian aid, water pumps and generators have arrived from Russia and several European Union member states, including Britain, Germany and Austria, as well as Serbia and Bosnia's fellow former ex-Yugoslav republic Montenegro, Croatia and Slovenia.
Authorities say the economic impact of the floods will be huge, devastating the agricultural sector that is vital to both the Serbian and Bosnian economies. (Writing by Matt Robinson; Editing by Andrew Heavens)