Football fans are being warned not to buy tickets for the Champions League final on the street as they could be stolen.
Police in Cardiff warned that tickets sold on the street may not give access to the match after a number were stolen from a hotel.
An image of a man police want to speak to in connection with the theft has been released as tens of thousands of supporters from the UK and Europe are set to arrive in the city for Saturday night's final when title-holders Real Madrid will take on Juventus.
The Welsh capital is gearing up to host the biggest sporting event in its history and a huge multi-agency security operation is under way to keep the 200,000 fans expected to visit the city this weekend safe.
Commenting on the ticket theft which took place at 4.20pm on Thursday at a hotel near Cardiff Airport, a spokesman said: "People are reminded that ticket touting is illegal, if people buy tickets off the street they probably won't give them access to the match as any stolen tickets are cancelled."
The long-awaited clash between the two European clubs will take place at the 74,500-capacity Principality Stadium - which will be renamed the National Stadium of Wales on the night as Uefa regulations ban the commercial title of a non-tournament sponsor being used.
On Friday, last minute preparations were still under way in the city centre and there was already a heavy police presence both of armed and non-armed officers, along with facial recognition teams, who are using the technology to monitor people on pre-determined "watch lists", which may include wanted or missing persons.
South Wales Police has said 6,000 police officers will be deployed in the city over the four-day period of the Uefa Champions Festival, which kicked off yesterday in Cardiff Bay and will end on Sunday, while 2,000 more officers will be in Cardiff on Saturday alone.
In the wake of the suicide bomb attack on Manchester, assistant chief constable Richard Lewis said the force had been planning for the event since it was announced and those plans would not be changed because they already contained ''a response which takes into account such atrocities''.
Meanwhile the city has been transformed by posters, banners and other decoration, all celebrating the event.
Cardiff Castle has been decked out in Champions League flags with banners depicting players hanging from the ramparts, above which sits a large blue dragon guarding a trophy.
A giant poster of Welsh football hero Gareth Bale, who will be hoping to start for his team Real Madrid on Saturday, overlooks the stadium.
Across the road, hoardings advertising Walkers crisps and a large screen cover one side of the NCP car park on Westgate Street.
Further down the road towards Cardiff Central, where trains will provide additional seats for up to 60,000 passengers, police officers were setting up a mobile police station.
Those travelling by rail from Manchester, Birmingham and London will be joined on board by British Transport Police (BTP) officers as part of the massive security operation aiming to keep the event safe.
Firearms officers will be posted at key stations across the country - the first time this has happened outside of London for a major event - and police dogs will also be deployed, the force said.
Assistant chief constable Alun Thomas, from the BTP, said highly-trained firearms officers would also be on patrol in Cardiff but that the deployment was not in response to intelligence and had been planned for some time.
He said: "Passengers are the eyes and ears of the rail network and with many thousands of extra people travelling to Cardiff, I'd urge them to stay vigilant and report concerns to us."
Some fans from Italy and Spain have already arrived in the city, many of them queuing up to take possession of their official tickets and lanyards.
French supporters in the city following Thursday night's Women's Final at the Cardiff City Stadium when holders Lyon beat Paris Saint-Germain on penalties, were enjoying the sights of the city and finding time to chant and sing football songs in the streets.
Responding to reports that homeless people had been asked to move out of the city centre for the weekend's festivities, assistant chief constable Richard Lewis said that was not the case.
He said: "There has been no direction given to police officers to ask homeless people to move away from the city centre.
"Police officers, dealing with homeless people, who are often vulnerable, provide as much support as possible and always signpost individuals to agencies for further help.
"There are general powers available to us to ask people to leave an area, in relation to crime or antisocial behaviour (Section 35).
"However, we can confirm that within the last 48 hours, these powers have not been used by any officer."
A number of homeless people sat on Queen Street said they had not been approached by police to move.