Police have charged four men who allegedly tried to stowaway out of Victoria on a freight train overnight.

The freight train had departed Melbourne at 10.30pm yesterday, bound for Perth.

South Australia Police officers were called when the four men, believed to be Victorians, were seen onboard the train when it stopped at Adelaide Freight Terminal at Regency Park this morning.

Police have charged four men who allegedly tried to stowaway out of Victoria on a freight train overnight. (9News)

Police swooped on the train yard, with police dogs Axe and Zac who quickly located the four men.

The men, aged 22, 26, 29 and 29 were arrested and charged with breaching COVID-19 restrictions.

They were refused bail and are expected to appear at Adelaide Magistrate's Court tomorrow.

All other states and territories have closed their borders to Victoria, particularly residents in greater Melbourne or the Mitchell Shire, with returning travellers legally required to fill out a declaration stating their reason for entering the state and being required to enter a 14-day quarantine if passage is approved.

Thousands of police are currently patrolling state and territory borders to ensure nobody from Victoria's hotspots leak through.

Businesses across greater Melbourne that were able to recently reopen were again forced to close back down, including gyms, salons, swimming pools and libraries.

The men were seen onboard the train when it stopped at Adelaide Freight Terminal at Regency Park this morning. (9News)Read More: What are the current border restrictions for each state and territory?

Cafes and restaurants can remain open but for takeaway only.

Greater Melbourne and the Mitchell Shire were placed back on level three restrictions on July 7, following a large rise in infections in those areas.