A shooter killed three people at a shipping company in Athens before turning the gun on himself. Police said the suspect was a disgruntled former employee.
Greek media reported that the shooter had killed two men and a woman before killing himself.
Emergency services arrived on the scene at the European Navigation company's offices.
EKAM anti-terrorism forces were the first to enter the building after the incident, at around 11:15 a.m. (0915 GMT), according to Greek newspaper Proto Thema.
What we know so far
The suspect was found dead next to the hunting rifle that was believed to have been used in the shooting, Greek newspaper Kathimerini reported. A pistol was also found in the suspect's car outside the office building.
News channel ERT reported that the suspect was a 70-year-old former employee who had recently been fired.
The owner of the company was among the dead.
"The suspected perpetrator, who worked for the family, was found dead in a different area from the three deceased people at the company. He had his assault weapon next to him and appears to have shot himself in the head," Police spokesperson Consantia Dimoglidou said.
Police also found two women, unharmed, who had been locked in a bathroom during the attack.