Poland began two days of mourning on Sunday, a day after a gunman killed six people and wounded 15 others in Krakow's main market square.

The attack occurred in Main Square (Rynek Glowny) in the Old Town of Poland's second-largest city on Saturday. The area is a popular tourist attraction.

In addition to the six people killed in the square, three bodies found at the suspect's home were the bodies of his sister, mother and father, police said Sunday.

Polish Prime Minister Donald Tusk has labeled the attack an act of far-right "terrorism," but authorities have not given a possible motive.

Poland's national prosecutor's office said it had launched an investigation into Saturday's shooting, saying that it constituted a suspected "terrorist offense."

Mourners left candles in the square to pay tribute to the victims of the shooting. Black flags and Polish national flags with black ribbons were also seen in the city.

The square remained partially sealed off on Sunday morning as authorities continued investigations.

What do we know about the shooting in Krakow's Main Square?

The 24-year-old suspect, who was wearing military fatigues at the time of the attack, allegedly shot at people at random as he drove around the square.

He was wounded by police and is in critical condition in hospital.

Polish authorities say the man held right-wing extremist and ultranationalist views.

"Everything indicates that he was fascinated by far-right ideologies," Interior Minister Marcin Kierwinski said at a news conference.

A British national was among the dead, and among the wounded were citizens of Austria, the United Kingdom, Germany, Portugal and Russia, according to authorities.

Two police officers were wounded while confronting the suspect and are in hospital. Officials have launched an appeal for blood donations for one of the officers, who is in critical condition.

The Krakow Carriage Driver's Association told Polish news agency PAP that several horse-drawn carriage drivers were seriously injured in the shooting.

Police confirm three bodies found were members of suspect's family

Police said on Sunday that three bodies found at the suspect's home were those of his sister, mother and father.

The family home is in the town of Ostrowiec Swietokrzyski, around 150 kilometers (93 miles) northeast of Krakow.

Police said that several firearms were seized from the apartment.

The suspect had no previous criminal record, according to Polish media reports.

He and his father were members of a shooting club.