Bucharest police spokesman said Christian Ciocan said one tree fell on the street near the center of the city and blocked traffic.
Fallen tree branches also hurt traffic across the city and several parked cars are reported to have been damaged.
Romanian President Traian Basescu, who returned from a three-day official visit to Israel, was stuck at the airport for about 15 minutes because of the storm.
Meteorologists issued a code yellow warning forecasting heavy rain across the country and put 21 counties under flood advisory.