A British citizen was among six people killed in a mass shooting in the heart of Krakow as investigators examine whether the gunman was motivated by far-right extremism.

The attack unfolded in the Polish city's historic Main Square on Saturday afternoon, sending crowds of tourists and residents scrambling for cover as shots rang out across one of the country's most popular visitor destinations.

The suspected attacker, a 25-year-old Polish national, remains in hospital after being shot during a confrontation with armed officers.

The identity of the British victim has not yet been released.

Polish police commander-in-chief Marek Boron said the dead included three Polish citizens, one British citizen and two people who had not yet been formally identified.

Addressing reporters alongside Polish Prime Minister Donald Tusk on Saturday evening, Mr Boron said: "There are 16 people injured including two police officers and the perpetrator himself.

"There are six fatalities, four women and two men - three Polish persons, one citizen of Great Britain and two persons who are not yet identified."

As the investigation widened, police carried out searches linked to the suspect and made a grim discovery away from the city centre.

Mr Tusk revealed that three further bodies had been found at the alleged gunman's family home in another city around 93 miles from Krakow.

Police later confirmed the victims were believed to be the suspect's parents and his 21-year-old sister.

The findings have intensified scrutiny of the suspect's background and possible motives.

Polish Interior Minister Marcin Kierwinski said investigators believed the attacker held "very radical views" and had become fascinated with "far-right ideologies".

Authorities have not publicly identified him and have yet to announce any formal charges while he remains under medical treatment.

According to police, the gunman opened fire at around 3.30pm using an automatic weapon in Krakow's Main Square, a landmark surrounded by restaurants, shops and historic buildings that attracts millions of visitors each year.

Officials said he moved between several locations within the square, firing repeatedly before police intervened.

Witnesses described scenes of panic as people sought shelter wherever they could.

Jonathan Balshaw, from Ipswich, was visiting the city with his girlfriend when the shooting began.

Speaking to the BBC, he said: "We ran down the side of the church and through the side door and hid with several other people until the gunfire died down.

"A lot of shots were fired, more than 20 with it sounding like multiple different firearms."

The suspect was eventually wounded in an exchange of fire with officers and taken to hospital for surgery.

Among those injured were two members of the police force who responded to the unfolding attack.

Polish Defence Minister Wladyslaw Kosiniak-Kamysz described the shooting as an "act of terror" directed against the people of Krakow.

The attack has prompted an outpouring of sympathy from Britain and across Europe.

As confirmation emerged that a British national was among those killed, Prime Minister Andy Burnham said he was "shocked and saddened" by the violence.

He said: "My thoughts are with the families of those who have lost their lives, everyone injured and all those affected by this senseless violence.

"The United Kingdom stands in solidarity with the people of Poland."

Foreign Secretary Ed Miliband also paid tribute to the victims.

In a statement he said: "The UK Government deeply mourns the British national and other victims who have died after the appalling attack in Krakow.

"All of my deepest condolences go to the families of the victims. The UK stands resolutely in solidarity with the people of Poland."

The Foreign, Commonwealth and Development Office said British nationals in Krakow should continue to follow the advice of local authorities and monitor local media.

Krakow mayor Lukasz Gibala announced the city would observe an official period of mourning until November 11 as residents come to terms with one of the deadliest attacks in the city's recent history.

Investigators are continuing to examine the suspect's movements, online activity and personal background as they seek to establish exactly what led to the shooting and whether anybody else may have been involved.