Traditionally dressed Croatian dancers celebrate at the Bajakovo border crossing between Serbia and Croatia early July 1, 2013. [Photo/Agencies]

People observe fireworks during a celebration of Croatia entering the EU, at the bordercross in Bregana early July 1, 2013. [Photo/Agencies]

Seven years of reform

Serbian President Tomislav Nikolic, once a fierce advocate of the "Greater Serbia" ideology that helped fuel the wars in Croatia and neighboring Bosnia, was among them, underscoring the change the region has undergone.

"We don't want Europe to stop at our borders, it must be open to other countries," Croatian President Ivo Josipovic told the ceremony.

To join, Croatia has gone through seven years of tortuous and often unpopular EU-guided reform.

It has extradited more than a dozen Croatian and Bosnian Croat military and political leaders charged with war crimes, sold shipyards steeped in tradition but deep in debt, and launched a fight against graft that saw former prime minister Ivo Sanader jailed.    

The country's Adriatic coastline, from the hills of Istria in the north to the medieval city of Dubrovnik in the south, has become a magnet for some 10 million tourists every year.

But a biting recession has left one in five Croatian workers jobless and taken much of the shine off the country's EU accession.

"Europe is all about work, work, work, no joy, no warmth," said Agata Miletic, a mother of seven who came to the ceremony. "When you hear that some countries want to leave the EU, that they have no money, you can't be optimistic."

Pop mixed with opera and traditional music in a colourful ceremony replete with white-clad dancers and a rousing rendition of Ode to Joy, the anthem of the EU.

Van Rompuy and European Commission President Jose Manuel Barroso were among some 170 foreign officials, including 15 heads of state and 13 prime ministers. One notable absentee was German Chancellor Angela Merkel, who had said she was too busy to attend.

Croatian media linked the no-show to a row over a former Croatian secret service operative wanted in Germany, though a spokesman for Merkel denied this.