A gunman believed to have been inspired by far-right ideology killed six and injured more than a dozen in Krakow on Saturday.
Police said the attacker drove onto Main Market Square, the busy centre of Poland's second largest city, and began randomly firing at people.
The gunman, who was equipped with military-style weapons and attire, was shot and subdued by police, one of whom was critically injured in the process.
The 25-year-old male Polish gunman - described by one minister as "ultra-nationalist" - survived and is in custody.
Poland's Prime Minister Donald Tusk said three bodies were later found at the suspect's home.
He said: "Until now in Poland we haven't had such drastic cases of terrorism... that's what we have to call this cruel attack on people's lives here in Krakow."
A British national was confirmed to be among those killed during the attack on the square.
The rampage began shortly before 15:00 local time (14:00 GMT) in the historic centre of Krakow, an ornate square which has long been a draw for tourists.
Footage showed the attacker's vehicle speeding through the centre of the city, and people fleeing as the sound of gunfire rang out.
The glass front of shops were shattered by bullets and a tram was shot at during the attack, which police say lasted for around three minutes.
Images from the scene showed overturned tables and scattered belongings left behind as people ran for their lives.
Armed police officers pursued the attacker's car until it crashed, at which point they engaged him in a firefight.
Distressing footage authenticated by BBC Verify captured the moment a police officer confronted the suspect as he lay on the ground.
The officer, who is visibly injured, can then be seen falling to the ground.
A Polish minister later said one police officer was fighting for his life and a second was expected to recover from a less serious injury.
Tusk later named them as Senior Constable Jakub Kulik and Senior Constable Artur Morański - he said they "saved many lives" and called them "true heroes".
The centre of Krakow was locked down as police tended to at least 15 injured people.
Some buildings were later evacuated as the attacker's car was searched for explosive devices.
After police identified the gunman and searched his home, the bodies of two women and a man were found. Tusk said there was "much to suggest" they were the suspect's immediate family members.
The name of the gunman has not been confirmed but Polish authorities have said he was a 25-year-old Polish male.
Poland's Interior Minister Marcin Kierwiński said "everything suggests that he was fascinated by far-right ideologies" and held "ultra-nationalist views".
The gunman wore full military tactical gear during the attack and was described as having a military-grade weapon - but the government said he was not a member of the Polish armed forces.
More weapons and ammunition were found inside the attacker's car.
A massive armed police presence was deployed across Krakow on Saturday evening, as security measures were ramped up in the capital Warsaw and elsewhere.
Tusk vowed that any "possible supporters of the perpetrator" would be detained and appealed to the public for information.
Three of the people killed in the square were Polish, one was British and two have not been identified, officials said.
Of the fifteen injured, two were police officers and five were foreign nationals - the interior ministry said they were from Britain, Austria, Russia, Germany and Portugal.
UK Prime Minister Andy Burnham said he was "shocked and saddened by the appalling shooting".
Witnesses who were close to the attack described panic and confusion around the square as it unfolded.
Cezary, a 24-year-old Polish university student in Krakow, said he did not realise the loud bangs he heard were gunshots until he saw four bodies lying on the street.
"We were still hearing gunshots, a lot of people were screaming," he said, adding that he saw someone trying to resuscitate a person covered in blood on the ground.
Caitlin Shasby, from Newcastle in the UK, said she heard shooting from her hotel room and was told to take shelter inside as police "barricaded" the street outside.
Another witness told Polish news website Inertia: "I saw shots being fired from the driver's side window and smoke was coming out."
"I ran to the police station in the main market square - when I burst inside, it was full of people hiding on the floor."
A period of mourning has been declared in Krakow until 11 November.
