A school for adult learners in Adelaide has been shut over a concerning cluster of COVID-19 cases.

About 70 students of the Thebarton Senior College are in hotel quarantine after being identified as close contacts of a woman in her 20s who tested positive for the virus.

Another 1100 students and staff are considered casual contacts and must self-isolate for two weeks.

The cluster of the cases associated with the college has now grown to five.

Chief Public Health Officer Nicola Spurrier said the action to close the college was taken out of an abundance of caution and there was no suggestion of widespread community transmission of the disease at this stage.

“We are doing everything we can to keep this cluster under control,” Professor Spurrier said.

The Education Department is expected to release information on Friday on how students can continue with their courses.