The number of deaths due to floods that hit central and eastern Europe over the weekend rose to at least 16 on Monday, with seven confirmed fatalities in Romania.
Casualties were also recorded in Austria, the Czech Republic and Poland as a result of the torrential rain caused by Storm Boris.
Budapest is to shut roads near the river Danube, which runs through the Hungarian capital, citing the risk of flooding later this week.
Warnings are in force along more than 300 miles of the Danube – a main route for Europe’s river cruise industry.
The river is rising by about a metre every 24 hours, with Budapest’s mayor offering residents a million sandbags to protect against floodwaters.
The impact on the European river cruise sector remains unclear although some itinerary alterations and cancellations appear inevitable.
The flooding forced a river cruise ship with 142 people on board, mostly Swiss tourists, to dock in Vienna, Switzerland-based company Thurgau Travel was reported to have said.
Some tram lines will not operate, while roads along the river will be closed in the Hungarian capital from Monday evening.
Trains between Budapest and Vienna have also been cancelled.
The overflowing of the Danube caused flooding in the old town area of the Slovakian capital of Bratislava, with local media reporting that water levels exceeded 30ft and were expected to rise further.
Poland declared a state of natural disaster as prime minister Donald Tusk said one billion zloty (£197 million) would be allocated for flood victims, adding that Poland would also apply for EU relief funds.
The Foreign Office yesterday extended travel alerts from eastern Austria to also include parts of the Czech Republic and Poland, where an evacuation orders has been imposed on all 44,000 residents of the town of Nysa.
Updated travel advice for the Czech Republic said: “Heavy rain and flooding is causing severe disruption, especially in southern and eastern parts of the country. Check local conditions before you travel and follow the instructions of the Czech authorities if you are in these areas.”
The message for Poland was identical. It said: “Heavy rain and flooding is causing severe disruption in the Lower Silesia (Dolnośląskie), Silesian (Śląskie) and Opolskie Voivodeships in southwest Poland. Check local conditions before you travel and follow the instructions of the Polish authorities if you are in these areas.”
Storm Boris is forecast to track south, bringing heavy rain into regions of Italy such as Emilia-Romagna.