Nine workers on the assembly line at the Mini car factory in Oxford tested positive for coronavirus.
BMW, the owner of the plant, said it was “monitoring the situation” and the site remains open after “detailed” talks with Public Health England.
Production at the Cowley plant was halted in March because of the pandemic, but resumed on May 18.
BMW said it has made a “wide range of practical changes”, which are being monitored daily.
Eight of the nine affected employees are understood to belong to a section of the assembly line and were on the same shift. The other worker is also from the assembly line, but from another section.
A spokesman for the BMW Group (UK) said: “Before restarting production, we made a wide range of practical modifications and improved hygiene and personal cleaning routines, in addition to providing clear instructions to everyone on site, in order to minimize the risk of transmission in the workplace as much as possible.
“These measures, fully aligned with the government’s health and safety guidelines, are monitored daily, in the best interest of our employees.”
All tests positive for the NHS coronavirus were returned in the last week and all employees are self-insulating.
Public Health England said that anyone identified as a close contact for any positive case is being advised to isolate themselves for 14 days, even if they have no symptoms.
The city’s factory employs 4,500 people and produces 5,000 cars a week.
BMW took over the factory in 2001, but the cars have been built on site since 1913.
Last year, a 60 Minis convoy traveled through Oxford to mark the vehicle’s 60th anniversary.