How Adelaide's coronavirus cluster bloomed

An elderly woman was the first known case in the Adelaide coronavirus outbreak, which has risen to 18.

How the woman, aged in her 80s, caught COVID-19 is so far unconfirmed, but indications are it spread into the community from Peppers Waymouth Hotel, one of Adelaide's hotels being used to quarantine.

It is believed a cleaner from Peppers Waymouth Hotel caught the virus from a hard surface, not from direct contact with anyone in quarantine.

South Australia Premier Steven Marshall said the contagion by droplet could not be classified as a hotel quarantine breach.

It is believed the cleaner passed the highly contagious virus to security guards.

Since the elderly woman tested positive, she has transmitted the virus on to two family members.

Cases two and three are a man in his 60s and a woman in her 50s, one of whom is a child of the elderly woman.

The fourth case is a worker at Yatala Labour Prison in Adelaide's northern suburbs. That person is a close family contact of one of the earlier cases.

In just 24 hours, the Adelaide cluster spiralled to 17 cases.

Fifteen of the 17 in the cluster are all from the same family group.

SA reported just one new case in the next 24-hour period, taking the total cluster to 18.

However, that case is believed to be an employee at the Brompton Aged Care Home, in Adelaide.

There is also another inconclusive positive test from a Brompton Aged Care Home, 9News understands.

If that test is confirmed positive, that would bring the Brompton Aged Care Home cluster to four.

Victoria's aged care sector was ravaged by the virus.

LIVE UPDATES: The latest from the Adelaide cluster outbreak

READ MORE: One new COVID-19 case in SA as new restrictions now in place

Multiple shopping centres, shops, buses, supermarkets and schools have been flagged as potential close contact risk zones.

Anyone who visited the Emergency Department at Lyell McEwin Hospital between 5.30 pm Friday 13 November and 8.00 am Saturday 14 November is also a risk contact.

There are now over 160 people in South Australia in isolation and shutdowns have been enforced.

READ MORE: South Australia suspends international flights, imposes new restrictions

As of midnight, COVID restrictions were back in place in South Australia.

All international flights into Adelaide have been suspended and gyms and recreation centres are now closed.

Funerals, church services and weddings have capped limits, as do gatherings at pubs, clubs and restaurants, with a maximum of 100 allowed.