The coronavirus outbreak has forced the postponement of one of Murray Bridge's biggest social events.
Murray Bridge High School's year 12 formal will not go ahead on Friday night, the school advised on Monday afternoon.
Should conditions permit, it will be held later in the year.
The postponement was unavoidable in the wake of the federal government's ban on non-essential public events with more than 500 people in attendence, which came into effect on Monday to slow the spread of the coronavirus.
Authorities hope doing so will save many lives among the people most at risk: the elderly and those with chronic medical conditions.
Still, there were only 20 confirmed cases in South Australia on Sunday.
SA Health declined to clarify whether any were in the Murraylands, to protect patient confidentiality.
But a spokeswoman said the department would notify community members if there were any risk of transmission.
The gatherings ban, and a requirement for all international travellers to self-isolate for 14 days on arrival, have forced Australia's events, tourism and sporting authorities to think quickly in recent days, as government advice has changed on a daily basis.
The World Health Organisation characterised COVID-19 as a pandemic last Wednesday and SA Health chief executive Chris McGowan declared a public health emergency in South Australia on Sunday, granting authorities special powers to help contain the outbreak.
SA Health has advised everyone to practice good hygiene, including hand-washing and covering coughs, and "social distancing", avoiding personal contact with others; to stay home if unwell; and to otherwise maintain a normal routine, eating well and exercising.
While state schools will remain open unless a student or staff member tests positive to the virus, principals of those with more than 500 people on site have been asked to consider cancelling events, staggering lunch breaks and avoiding whole-school assemblies.
Decisions are expected in the coming days on the biennial Mallee formal for students from Karoonda, Lameroo, Coomandook and Tintinara, scheduled for Saturday night, and Unity College's formal, on March 27.
Development director Wayne Gehling said it might be possible to modify Unity's event instead of postponing it - for example, by foregoing the usual red carpet arrivals - but that the college was listening to both students and the Lutheran Schools Association.
Unity and St Joseph's School are among those to have cancelled upcoming sports days, as well.
Cycling event Revolve 24 was expected to go ahead on Saturday and Sunday at The Bend Motorsport Park, organisers said on Sunday.
But organisers said they would continue to take guidance from the federal Department of Health and Cycling Australia, as the health and wellbeing of everyone involved was their first priority.
About 230 riders had registered for the event.
The River Murray Football League had not yet made a final decision about whether the season would begin as planned on March 28, president Terry Connolly said.
"As you can appreciate, this situation continues to evolve and thus we are monitoring it closely in consultation with the SANFL," he said in a Facebook post.
"These are unprecedented circumstances and we appreciate your understanding.
"We will update you when there are further developments and encourage you to keep abreast of our social media channels."
The River Murray Netball Association's Tania Adler said that competition would also wait for direction from Netball SA.
She hoped round one's matches could go ahead, she said - "we're in the open air, we're in a small country area" - but the association would take a wait-and-see attitude for now.
Murray Bridge Basketball Association has suspended all its junior games until further notice.
- More information: health.gov.au/covid-19 or the National Coronavirus Hotline, 1800 020 080.