* Worst flooding in Balkans in over a century
* Death toll in Bosnia reaches eleven
* Rush to defend west Serbian town against rising water (Adds quotes, details)
By Marko Djurica
OBRENOVAC, Serbia, May 17 (Reuters) - Seven bodies were pulled from flooded homes in Bosnia and the army rushed to free hundreds of people stranded in a school in Serbia on Saturday during the worst floods to hit the Balkans in over a century.
Soldiers steered huge amphibious vehicles through streets under 2-3 metres of water in the town of Obrenovac, 30 km (18 miles) southwest of the Serbian capital Belgrade, trying to rescue an estimated 700 people crammed into the top floors of the Jefimija primary school.
"The whole town is under water," a Reuters photographer at the scene said. Up to 70 people at a time scrambled onto the vehicles, mainly women and frightened children.
Others, stranded in flooded homes, climbed from roofs and balconies into small boats to be taken to safety.
The town of around 30,000 people, located at a bend in the River Sava, has been the worst hit by days of heavy rainfall, unprecedented since records began almost 120 years ago.
Serbia's energy system was brought close to collapse, with power cut to 95,000 homes and capacity down by 40 percent.
Prime Minister Aleksandar Vucic said there were fatalities in Obrenovac, but authorities would not specify how many until the waters receded and the extent of the damage became clear. Three had been confirmed dead by Friday.
In neighbouring Bosnia, the death toll reached 11, with six bodies discovered on Saturday in the northeastern town of Doboj, and another In the northern town of Samac.
In Sabac in western Serbia, thousands of volunteers joined soldiers, police and firefighters working through the night to build sandbag flood defences against the rising waters of the Sava.
In the capital Belgrade, residents donated food, clothes and bedding. Police appealed for more boats. A steady rain fell on Saturday and more was forecast for Sunday.
'WAIT AND HOPE'
"Now we have to sit and wait, to wait for that next wave and to hope," Vucic told a joint news conference with Bosnian Serb leader Milorad Dodik.
Of the Bosnian death toll, Dodik said: "I'm afraid that won't be the end."
In the Bosnian border town of Bijeljina, authorities said they would evacuate 10,000 people. More than 15,000 have already been evacuated in Serbia.
"We left behind the car, motorcycle, tools, all our furniture, valuables," said Dragana Ilic, an Obrenovac resident evacuated to a shelter in Belgrade.
"We just grabbed our mobile phones and left. All our IDs were left behind. The whole house is under water."
Another evacuee from Obrenovac at the shelter, a student who gave her name as Katarina, said she was worried about her uncle. "I last spoke to him at around 11 (0900 GMT) yesterday, and since then I have no information on where he is or what he's doing," she said. "I only know that it's wet, cold, and there's no electricity or running water."
In Bosnia, helicopters evacuated people from the northern towns of Samac and Modrica and trucks and bulldozers carried food to the hardest hit areas.
About 1,000 people, including babies, pregnant women, invalids and elderly were evacuated from the region of Zeljezno Polje in central Bosnia, where hundreds of homes were destroyed in landslides.
"I think we'll never be able to return to our village," local Muslim imam Zuhdija Ridzal told Reuters by telephone from Zeljezno Polje. "It has disappeared".
On Friday Serbia's state-run power utility Elektroprivreda Srbije (EPS) trimmed output at its largest hydro power plant, Djerdap 1, on the Danube river by a quarter.
It also closed down 1,650 MW in capacity of its largest coal-fired power plant Nikola Tesla (TENT), on top of a 10 percent cut in total output a day before.
Flooding of the Kolubara, the Danube and the Sava rivers brought down cables and transformer stations, soaked coal depots that feed the power plant and caused a fire inside the Kolubara complex which had been shuttered since Thursday. (Additional reporting by Daria Sito-Sucic and Maja Zuvela in Sarajevo, Fedja Grulovic in Belgrade; Writing by Matt Robinson; Editing by Angus MacSwan and Raissa Kasolowsky)