Canterbury district commander Superintendent John Price said contract tracing was being undertaken at the man's place of work.
"One person was seen in breach of the alert level 4 restrictions at the Timaru Countdown on Wednesday afternoon," Price said.
"That person was spoken to by police and assessed to have made a poor choice rather than a deliberate decision to be irresponsible, and the individual was issued with a pre-charge warning."
Price said public health officials were advised and agreed with the warning, and were now checking in daily with the man.
"Contact tracing is continuing and testing of a number of contacts at the individual's workplace is now underway."
He said police continued to work with and support the Ministry of Health as the lead agency to ensure the safety of the community against the spread of Covid-19.
"Police ask that people think of others and always do what is right, kind and safe while police continue to be visible and deliver our top-tier service to all.
"We continue to urge people to follow the Government's advice on Covid-19 and stay home and save lives."
Under lockdown rules, any breach of the Covid-19 guidelines, which include that anyone confirmed to have coronavirus must self-isolate for 14 days, can incur a $1000 fine.
New Zealand has recorded 11 deaths from Covid-19 and 1422 cases at 1pm today. More than half of those infected with the virus have now recovered.
Seven of the deaths relate to a Canterbury rest home cluster of residents aged in their 70s, 80s and 90s with underlying health conditions.
Thirteen new cases were confirmed on Saturday.
Targeted testing of asymptomatic supermarket shoppers was announced on Friday in three regions across New Zealand, including the Waikato, Canterbury and Queenstown.
The alert level 4 lockdown is in place until the end of Wednesday. The Government is expected to advise on Monday whether or not it will drop to level 3 after that.