South Wales Police's facial recognition van will be in Cardiff city centre ahead of a major event for the city.
Thousands of people will be going to watch Beyoncé's concert and some fans already started queuing outside the city's Principality Stadium.
Police say one of the main reasons the van will be in the city centre will be to identify people wanted for "priority offences".
However, the decision has been criticised by campaigners, who say it is an "outrage" that the CCTV van is being used.
The move comes only a few weeks after the police force announced the van will be brought back into use.
South Wales Police had paused their use of the technology following a Court of Appeal judgement in 2020 that highlighted the need for more work confirming the software does not discriminate based on "race or sex".
Campaign group Big Brother Watch called the decision an "outrage" saying: "Live facial recognition is a dangerously authoritarian mass surveillance tool, subjecting ordinary members of the public to high-tech police lineups."
Mark Johnson, Advocacy Manager at Big Brother Watch, added: "South Wales Police's own stats show live facial recognition to be around 90% inaccurate, with studies showing that innocent people of colour are more likely to be misidentified as potential suspects.
"It is an outrage that South Wales Police have chosen to deploy live facial recognition at Beyonce's Renaissance show, which celebrates diversity. They should reconsider and drop their plans to use this rights-abusive technology on innocent members of the public this evening."
Police stated the other reasons why the van is being used. They include:
To support law enforcement including the administration of justice (through arrest of persons wanted on warrant or unlawfully at large/ recall to prison)
To ensure and promote the safeguarding of children and vulnerable persons at risk
As well as several road closures and diversion of traffic, there is also large disruption on the rail network due to engineering works taking place.
Replacement buses are running instead of trains on the Rhondda, Cynon and Merthyr Tydfil lines down to Pontypridd. Trains are running between Cardiff and Pontypridd but Transport for Wales said it expects these services to be "very busy".
Doors open for fans at 5pm but Beyoncé's performance kicks off at 7.30pm.
You can find the full list of road closures and what impact that is having on public transport here: