The worst flooding since records began has killed at least 20 people dead in Serbia and Bosnia and has forced tens of thousands to flee their homes.
The flooding is the worst since records began 120 years ago, according to meteorologists, who said it is due to the region getting three months of rain in just three days.
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The five living former US presidents appeared together for the first time since 2013 to raise money for hurricane victims.
Some 465 seats are up for grabs in the lower house, which Abe dissolved last month to call a snap election amid rising approval ratings.
Ministers are also looking at schemes such as “lock-in agreements” to reduce the 250,000 sales that fall through annually.