At least six people were killed and a dozen others injured when a gunman with suspected far-right ties opened fire in the center of Krakow, Poland's second largest city.
When police searched his residence, they found three other bodies.
Here's what's known so far.
How did the attack happen?
The attack began shortly before 15:00 local time (14:00 GMT) on Saturday (November 7) in Krakow's Main Market Square. This is the city's busy heart and a popular location with tourists.
Police said a man drove into the square and began shooting "randomly" at people from his car.
Footage from the scene showed the crowd fleeing in panic and gunshots clearly audible.
In what appeared to be a random attack, a passing tram was hit and its windows were shattered, but no passengers were injured.
Officials said armed police officers rushed to the scene and exchanged gunfire with the suspect. The suspect was shot within three minutes of the attack, preventing further mass killing.
A 25-year-old man who was arrested remains in hospital after undergoing surgery for a gunshot wound.
Disturbing footage, verified by BBC Fact Check, shows a police officer confronting the suspect on the ground before firing multiple shots.
The officer then fell to the ground and appeared to be injured.
Shop windows in the square showed signs of damage, seemingly caused by bullets, with shards of glass scattered across the floor.
City officials are asking residents and visitors to stay away from the area while the investigation continues.
The police said that the suspect's car found at the junction of Dietra Street and Stradomska Street was inspected for explosive devices, but no explosives were found. During the operation, residents of nearby buildings were evacuated.
How many people were killed and injured?
Six people have been confirmed dead, including four women and two men, including a British citizen. Three of the dead were Polish and two others have not yet been identified.
16 people were taken to hospital, including five foreign citizens, two police officers and the attacker himself. The Polish Interior Ministry later stated that the foreign injured were from Austria, the United Kingdom, Germany, Portugal and Russia.
Polish Prime Minister Donald Tusk later announced the identities of the injured police officers, namely Senior Police Officer Jacob Kulik and Senior Police Officer Artur Molanski.
A Polish government minister said one of the police officers was shot three times while arresting the attacker and was in "extremely critical" condition.
He added that the officer was undergoing surgery.
Polish authorities have not yet released the names and ages of the other dead and injured.
Tusk said that when police searched the shooter's residence, they found three bodies, including two women and a man.
What do we know so far about the suspect’s identity and motives?
Police identified the attacker as a 25-year-old Polish man but have not yet released his name.
A police spokesman said the suspect was wearing "military-style clothing" and had military-grade weapons, but authorities pointed out that he was not a soldier.
"A large amount of weapons and ammunition were found in the vehicle," the spokesman added.
Polish media reported that the suspect held a firearms license and may have obtained the relevant weapons from his family's residence.
One minister said preliminary investigations showed he was inspired by "far-right ideology".
The minister also described him as an "ultra-nationalist" but gave no further details.
His residence in Ostrowitz-Shivientokrzyski was searched. The city is about 200 kilometers from Krakow, and counter-terrorism police also participated in the operation.
How did witnesses describe the attack?
The shooting took place in one of Europe's largest medieval squares. The location is busy and is a popular tourist destination.
Jonathan Balshaw, from Ipswich, England, was at the scene with his Polish girlfriend Dominika. The two men were outside the Basilica of Our Lady in a corner of the square when the shooting occurred.
"We ran along the side of the church, went in through the side door and hid with a few other people until the gunfire died down," Jonathan said.
"Many shots were fired, over 20 shots, and it sounded like it was coming from multiple different firearms, with two distinctly different sounds."
Caitlin Shasby, from Newcastle, arrived in Krakow on Friday with her friend Jon for a long weekend break.
She said the two heard gunshots in their hotel room but initially had no idea what was going on until the hotel called them to tell them to "remain in the room until further notice."
How did Poland and the international community react?
Prime Minister Tusk said after traveling to Krakow: "Until now, there has never been a terrorist incident of this magnitude in Poland... This is how we must call this brutal attack that claimed lives in Krakow."
Kraków Mayor Vukáš Djbava has signed an order declaring that the city has entered a period of mourning that will last until Wednesday (11th).
British Prime Minister Beander said: "I am shocked and saddened by the horrific shooting in Krakow today."
He added: "My thoughts are with the bereaved families, all the injured and all those affected by this senseless violence. The UK stands with the people of Poland."
British Foreign Secretary Moon Lippin said on social media that the British government expressed "deep condolences" to those who lost their lives in this "appalling attack."
