The 600m-long cable-stayed bridge will cross the Danube to link the Hungarian town of Komárom with Komárno in Slovakia.
"Today's event is a good example of the fact that the Danube does not separate us, Hungarians and Slovaks, but connects us with each other," said Hungary's prime minister Viktor Orbán.
The US$107 million bridge has a single 94.5m-tall pylon. It is being built by the HM Dunahid consortium, made up of Hídépíto and Mészáros & Mészáros. Completion is due in autumn 2019.