Twenty people have been injured in the Iranian city of Astara after the heaviest rains in 100 years, local officials have said.
Floods have also hit the neighbouring city of Talesh, also on the Caspian Sea coast near Azerbaijan.
"Heavy rains ... have fallen over Astara which have not been seen in 100 years," Gilan province's head of crisis management Amir Moradi told the ISNA news agency.
Almost 100 people were killed in flash floods that swept across the country last year, affecting 21 out of 31 provinces.
More rain is expected on Tuesday in the country's Gilan and Manzandaran provinces.
Footage on social media showed rescuers using small boats to move around Astara, where bridges and roads collapsed.
The river systems that flow from Iran's extensive mountain ranges make it vulnerable to flash flooding.
It is particularly vulnerable to climate change and has also battled extreme heat this summer.
Last month, government offices and banks shut for two days due to "unprecedented heat" as temperatures hit 50 degrees in the south-west.
Dust storms have led to hundreds being taken to hospital.
Severe water shortages, a long-term problem in Iran, have also worsened.
The Iran Meteorological Organisation estimates 97 per cent of the country faces issues with some level of drought.
Locals in Tehran and Karaj faced significant water shortages earlier this summer, which have previously led to protests and unrest.