The first to arrive at the biggest presidential conference ever held in Croatia was Moldovan President Vladimir Voronin, who arrived on Wednesday.
The first to arrive today was Italian President Carlo Azeglio Ciampi.
Also attending the summit will be Alfred Moisiu of Albania, Heinz Fischer of Austria, Ivo Miro Jovic of Bosnia and Herzegovina, Georgi Parvanov of Bulgaria, Vaclav Klaus of the Czech Republic, Laszlo Solyom of Hungary, Branko Crvenkovski of Macedonia, Aleksandar Kwasniewski of Poland, Ivan Gasparovic of Slovakia, Janez Drnovsek of Slovenia, Svetozar Marovic of Serbia and Montenegro, and Traian Basescu of Romania.
The host of the summit is Croatian President Stjepan Mesic, while Valdas Adamkus of Lithuania will be a special guest.
Numerous state delegations, representatives of international organisations and business people are also expected at Westin hotel, where all the delegations will stay. Security measures are very high.
German and Ukrainian presidents Horst Koehler and Viktor Yushchenko will not attend, the former because Germany is forming a new government and the latter due to health reasons.
About 200 foreign and 200 Croatian journalists have been accredited to cover the event. Their press centre will be in Mimara museum, which is just across the Westin.
The summit's programme also envisages bilateral meetings.
Today the guests will attend a performance of the "Jalta, Jalta" musical at the Croatian National Theatre.
Two plenary sessions will be held at the summit. The first, on how to complete the European integration process, will be opened by President Mesic on Friday, while the second, on a social and economic model appropriate for united Europe, will give participants an opportunity to discuss the topic with business people on Saturday.
On Friday afternoon the participants will make a trip to Trakoscan castle, 50 km north of Zagreb, where they will attend a concert by the Croatian Baroque Ensemble.
The idea of holding an informal meeting of Central European presidents was born at the opening of the Salzburg Festival in July 1993, which was attended by the then presidents of Austria, Germany, Hungary and the Czech Republic.