SYDNEY: Two teenagers have been charged with planning an attack at a school in Australia using guns and explosives in an act police Wednesday alleged was designed to harm "a large number of people".

The plot targeting the school in South Australia's Riverland region came to the attention of authorities earlier this month with the two young men arrested soon after.

Detective Superintendent Des Bray said they were accused of planning "an attack at a school involving the use of firearms and explosives which could have led to multiple deaths".

"Two teenage boys -- aged 16 and 18 -- are in custody. The younger has been charged with a count of solicit to murder, while the older teenager has been charged with aggravated counts of threatening to kill," he said.

"There is no evidence to show that any other person was linked with this matter, nor did the two individuals have possession of firearms."

The alleged plot was foiled a day after police in Melbourne arrested a 20-year-old man who they claimed was planning to buy a gun and kill as many revellers as possible on New Year's Eve in the city.

Police said that man, Ali Ali, was an Islamic State sympathiser, but there was no mention of any extremist group link to the teenagers in South Australia.

Bray said it will be alleged the pair were involved in planning the attack between June 1 and November 7 this year.

The main towns of the fruit-producing Riverland region northeast of Adelaide include Renmark, Berri, and Loxton-AFP