* Worst rains and floods for at least 120 years
* More than 100,000 without electricity in Serbia
* Thousands evacuated from homes
By Fedja Grulovic
OBRENOVAC, Serbia, May 16 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.
At least four people have died in the disaster. Thousands have been evacuated from homes in central and western areas of Serbia. Around 135,000 households were without power across the country and the government approved emergency electricity imports. Another 65,000 were without electricity in neighbouring Bosnia.
"This is a catastrophe. Nature has never been so cruel to us," Serbian Energy Minister Aleksandar Antic said.
The heaviest rains since records began almost 120 years ago have hit Serbia and Bosnia this week. Three people, including a rescue worker, drowned in Serbia and a villager died in a landslide near the northern Bosnian town of Bjeljina.
The deluge has made many hillsides unstable in the mountainous region. Several people were injured when dozen of houses were destroyed by a landslide on the edge of the Bosnian capital Sarajevo.
Bosnia's Centre for the Removal of Landmines warned that mines laid during the country's 1992-95 war could be moved by floods and landslides.
FLEEING ON FOOT
In the village of Topcic Polje, near the central Bosnian town of Zenica, a landslide devoured dozens of houses and water flooded the main road.
Villagers fled on foot along railway tracks with bags and babies in their arms.
"The people are walking to Zenica, all the roads are jammed, we are stuck here and there is no help from anyone," villager Asim Skopljak told Reuters by telephone from Topcic Polje. "There is no electricity and no drinking water."
Surges of high water were expected to reach the major rivers Sava and Danube later in the day and over the weekend, threatening thousands more people and roads, meteorologists in Serbia said.
Bosnia's central government appealed on Friday for international help. Russian emergency teams with rescue boats arrived in Serbia on Friday and were heading for Obrenovac to help with the operation there.
Israel, Turkey, Slovenia, Croatia and Austria have also approved the sending of aid including helicopters and boats. International peacekeepers' helicopters were also ready to help rescue operations in Bosnia. (Additional reporting by Ivana Sekularac, Daria Sito-Sucic, Maja Zuvela and Dado Ruvic; editing by Zoran Radosavljevic and Andrew Roche)