Elektroprivreda Srbije's (EPS) Nikola Tesla coal-fired power plant in Obrenovac, which supplies electricity for half of Serbia, has been hit by flood water as the Sava river swells.
Sandbags have been stacked by soldiers and energy workers to protect Serbia's biggest power plant from flood waters.
According to Reuters, another ten trucks stacked with sandbags were standing by. The Belgrade authorities said that emergency services and volunteers had filled 60,000 bags and transferred them to the power plant.
Meanwhile, thousands of people were evacuated in neighbouring Bosnia, Reuters reported, citing Bosnian state radio.
The Sava river has disturbed the regions of Serbia, Bosnia and Croatia in total.
The death toll from Serbia's worst rainfall in more than a century has reached 35.
EPS spokeswoman Djina Trisovic said that some employees at the Nikola Tesla plant had worked three days with barely a break because their relief team could not reach the plant.
"The plant should be safe now. We've done all we could. Now it's in the hands of God," Trisovic said.
EPS had already closed all the units as a precaution measure, but it is estimated to be powered down completely if the waters breached the defences.
EPS executive board head Aca Markovic said that the situation was under control at the Kostolac coal-fired power plant located east of Belgrade.
EPS spokeswoman said, "New sandbag barriers have been put up as a precaution in Kostolac and all water has been diverted into an old riverbed of the Mlava."