Passengers on the bus were hurt and one passenger was treated for severe trauma, local reports said.
Drivers left their cars to stare at the rare tornado as it swirled through fields, picking up a tower of dust.
The tornado narrowly missed a village Calarasi but 10 buildings lost their roofs.
The freak weather early on Tuesday evening was a result of a cold front from Bulgaria, to the south, which collided with far warmer, moist air in southern Romania, said meteorologists. The tornado's speed was estimated at 90km/h (56mph).
"We're really talking about a great and powerful tornado that has formed as a funnel from top to bottom and bottom to top," meteorologist Mariana Fratila told Adevarul newspaper.
Drivers posted videos of the tornado on social media as they drove past the swirling funnel of dust.
Earlier multiple tornadoes hit the Turkish city of Antalya, the country's southwestern region, according to Severe Weather Europe.
Up to five tornadoes have been reported. Significant damage is observed at Antalya airport: planes were damaged by moving and flying debris, vehicles, including an airport bus, hit and damaged.
Serious damage was caused both to the city center and its surroundings.
The Severe Weather Europe notes that at least 12 people were injured at the airport; they were in one of the buses that crashed into a plane because of a tornado.
According to preliminary calculations, more than 200 buildings were damaged in the city, CNN Turk reports.