The heroin was discovered overnight in 500-gram packages hidden in secret compartments in the trailers of three trucks that were inspected at the port's ferry terminal.
"The three trucks have license plates from Bulgaria's capital, Sofia, but came to the port of Burgas through the ferry service connecting Burgas with Georgia's Black Sea port of Poti," the website cited the Bulgarian Interior Ministry as saying.
Bulgaria is a major gateway for drugs smuggled to Western Europe.
In a second development, customs officers seized 78 kg of heroin after a check on a Polish car at the Kapitan Andreevo checkpoint on Bulgaria's border with Turkey.
The 150 packets of drugs were hidden in secret compartments in the car, which was driven by a 50-year-old woman traveling from Turkey to Germany. Police said the drugs had a street value of more than 3.5 million euros.