South Australia is going into a hard lockdown for six days, mandating masks in public and banning funerals to control its COVID-19 outbreak.

Schools, cafes and factories will close from midnight on Wednesday and all outdoor exercise will be prohibited.

GP practices and other medical services will be allowed to remain open, but people will otherwise have to stay home unless accessing or providing essential services, with shopping trips limited to one person per household per day.

A cluster linked to hotel quarantine in Adelaide has risen to 22 cases, sparking the initial lockdown which will be followed by eight days of further restrictions.