Poland has begun two days of national mourning after a 24-year-old man with far-right views drove into a busy central square in Krakow and opened fire, killing six people and wounding 15 others before police shot and wounded him.

The attack, which Poland’s defence minister described as an “act of terror”,” happened on Saturday in Main Square, in the heart of Krakow’s Old Town.

It is a major tourist hub in the country’s second-largest city.

By Saturday night (local time), mourners had left candles in memory of the victims. The square remained partially closed on Sunday morning as authorities continued their investigation.

St Mary’s Trumpet Call, a traditional five-note melody played every hour from the highest tower of St Mary’s Basilica on the Main Square, was paused overnight in tribute to the victims. It was the first time the call had been missed since World War II.

Authorities also found the bodies of the assailant’s sister, mother and father at the man’s family home in Ostrowiec Świętokrzyski, a city about 150 kilometres north-east of Krakow. They likely died from gunshot wounds.

Marie-Ange Collaer wrote on Facebook that she and her family survived the shooting during a trip to Krakow from Brussels.

“We literally ran for our lives and managed to hide from the bullets flying around,” she wrote.

“Lying on the floor in a shop like in a bad police movie whilst you hear bullets everywhere.”

British resident Neil Thaxton and his wife were also witnesses to the attack.

“We had just walked through the main square and heard the gunshots,” Thaxton wrote on Facebook.

“We thought it was fireworks then people started running, we went into a gift shop and the staff took us in the back of the shop and locked the doors and turned the lights off.”

Prosecutors say they have opened an investigation into the murder and attempted murder of numerous people, including police officers, with the act “constituting a terrorist offence.”

Four women and two men were killed in the Main Square shooting. Three of the women and one of the men were Polish, Krzysztof Jan Klęczar, the Malopolska regional governor, said on Sunday. A man from Britain and a woman from an unidentified foreign country were also among the dead.

A video posted on social media showed a police officer repeatedly shooting the attacker, who was lying on the street. The officer later slowly collapsed to the ground.

The two police officers who stopped the gunman, in actions authorities hailed as heroic, remain in the hospital. They were both conscious by Sunday.

“If it weren’t for the efficient and selfless intervention of these two young men, the number of victims could have been significantly higher,” Klęczar said.

Michał Pędziwiatr and Mateusz Wierdak, two local surgeons who were dining nearby, also stepped in. Wierdak “took care of the officer who subdued the attacker because he truly needed urgent help”, Pędziwiatr told Polish news website onet.

“Without protection, without gloves, he simply focused on the officer, stopping the bleeding in his chest. This probably saved his life,” he said.

Five foreigners are among the wounded. They come from the UK, Portugal, Russia, Germany and Austria.

The suspect is also in critical condition after multiple surgeries.

Interior Minister Marcin Kierwiński said the suspect held “very radical” and “ultranationalistic” views.

“Everything indicates that he was fascinated by far-right ideologies,” Kierwiński said.

Local officials in Ostrowiec Świętokrzyski said they seized seven weapons from the family home. Along with four found on the suspect or in his car in Krakow, that brought the total number recovered to 11.

Both father and son had gun permits, they said.

Mass shootings are uncommon in Poland. However, in mid-October three attacks at schools in the central province of Mazovia took place within four days, leaving one person dead and many wounded.