It was not for police business, according to the source.
While police wouldn't confirm any specific details, a spokesperson confirmed an investigation was under way into an alleged border breach.
"Police [are] conducting an internal investigation following an alleged police decision to allow travel through a boundary checkpoint without an appropriate exemption.
"As police currently understand it, this involved a member of police accompanying a group of people across an alert level boundary so they could attend a burial a short distance away.
"Police have confirmed the travel was not permitted ... but further inquiries into the matter are required to more fully understand the context, including decision-making around the case."
Auckland has been in alert levels 3 and 4, which carry stiff travel restrictions, since it was announced in August that the highly infectious Delta variant of Covid-19 had escaped into the community.
More than 320,000 vehicles have been stopped at checkpoints on the city's southern and northern boundaries in that time, police noted this evening in the organisation's daily compliance update. Of those, 5524 have been turned around.
Police have also noted over the past month multiple arrests for people crossing the border in breach of lockdown rules - the most notable being a couple accused of using their essential worker exemptions to drive to Hamilton before taking a flight to a holiday home in Wānaka.
Other high-profile breach cases have included:
• A 53-year-old arrested at Wellington's ferry terminal after police said he crossed Cook Strait with a caravan he'd bought in Christchurch, after misusing work exemption to leave Auckland.
• A woman, 24, and man, 41, arrested in Wellington after allegedly travelling from Auckland.
• Two Aucklanders accused of using false documents to visit Taupō.
• Three essential workers from Auckland allegedly caught at Mt Ruapehu's Turoa Ski Field.
• A man who boasted on TikTok of making a cross-border McDonald's run.
• Two gang associates accused of trying to flee police on a gravel road near the lockdown border. The pair were later found to have over $100,000 in cash in the car and a boot full of KFC, police said.
"It's important to remember that travel across an alert level boundary remains restricted and you will be turned away if you don't have the required evidence for permitted travel, as outlined on the Covid-19 website," police said in today's border compliance update statement.