A Victorian man has been arrested in South Australia after allegedly stowing away on a freight train to cross the border.

A rail supervisor found the man after the train arrived in Adelaide about 6.15am on Wednesday and alerted police.

The man, 41, was quickly arrested by patrols and charged with breaching COVID-19 directions.

He allegedly boarded the train last night in Dimboola, Victoria.

SA Police say the man submitted a Cross Border Travel Registration form but did not wait to find out if his entry was approved.

He was refused bail and is expected to appear in court later on Wednesday.