Earlier in the day, Nawrocki held talks with US Energy Secretary Chris Wright in response to what Polish officials say is Washington's growing interest in the region's economic resilience.
He also met Croatian Prime Minister Andrej Plenković ahead of the summit's opening plenary session.
A joint press conference with Plenković and Slovak President Peter Pellegrini was expected on Tuesday afternoon, with an official dinner to follow in the evening.
Talks will continue on Wednesday at the Three Seas Business Forum.
Discussions at the summit are expected to cover road, telecoms and gas infrastructure, as well as a new investment fund aimed at drawing private capital into the region.
Italy is also set to be formally admitted as a strategic partner of the initiative, joining the United States, Japan, the European Commission and Germany.
Poland has brought one of its largest ever business delegations to the event, with more than 50 entrepreneurs flying to Dubrovnik on the presidential aircraft.
The Three Seas Initiative was founded by Poland and Croatia in 2015 and now groups 13 EU member states stretching from the Baltic to the Adriatic and the Black Sea.
Its first summit was held in Dubrovnik in 2016.
(ał)
Source: PAP, prezydent.pl