SYDNEY:South Australia reported 14 new coronavirus cases on Monday, a rapid spike in the state's first outbreak since April, prompting officials to impose social distancing restrictions.

The cluster also prompted some other Australian states to reimpose strict quarantine measures on anybody arriving from South Australia - just days after Prime Minister Scott Morrison said he expected all internal borders to be open by Christmas.

South Australia authorities first reported three locally-acquired COVID-19 cases on Sunday, saying the outbreak was caused by a worker from a quarantine hotel infecting family members. By Monday, case numbers had jumped to 17.

"We are facing our biggest test to date," South Australia Premier Steven Marshall said, as he announced new social distancing rules and re-introduced restrictions at restaurants, cafes and gyms.

"We are working around the clock to stay ahead of this cluster. We cannot wait to see how bad this gets."

Marshall ordered the closure of gyms, recreational facilities, community sports and play cafes. The numbers of people at funerals were capped at 50, while church services were restricted to 100 people. Pubs, clubs and restaurants are capped at 100 people per venue, and a maximum booking of 10 people.

Marshall also advised people to work from home, avoid unnecessary travel and wear a mask where social distancing was not possible.

International flights will be diverted from Adelaide for at least the rest of the week, he added.

Australia had recorded several days with no new locally-transmitted cases since Victoria state came out of a lengthy lockdown to stamp out an outbreak there earlier this month.

Victoria has been responsible for the bulk of the around 28,000 cases in Australia and just over 900 deaths.

Prime Minister Scott Morrison said the latest outbreak was "a reminder, even after a lockdown, even after all this time, the virus hasn't gone anywhere".

Federal Health Minister Greg Hunt said he had offered to supply the national contact-tracing system and defence force personnel to help South Australia stop the virus from spreading.

Western Australia, Tasmania, Queensland and the Northern Territory all imposed mandatory quarantine for arrivals from South Australia.

Australia's most populous state of New South Wales (NSW) meanwhile did not immediately announce changes to its internal border controls.

Separately, Australia said it would spend A$1 billion ($726.3 million) underwriting construction of a vaccine manufacturing plant under a deal with a unit of biomedical giant CSL Ltd <CSL.AX>, guaranteeing supply of flu shots and antivenins.