Heavy rainfall over the past 48 hours has led to severe flooding in the central parts of the city. Rivers have overflowed their banks, and many streets are now impassable. Local authorities have issued an evacuation order for low-lying areas, and rescue boats are assisting residents trapped in their homes. Power outages are widespread, affecting thousands of households. The meteorological office warns that more rain is expected throughout the night, which could worsen the situation.
What is the most urgent warning mentioned in the news report?