A homeless man has been arrested as police investigate two alleged sexual assaults in Melbourne’s southwest.

The 39-year-old was arrested in Hoppers Crossing about 11.40am on Friday.

Police allege the first incident occurred about 11.30am on Thursday, when a man broke into a home on Whitsunday Dr armed with a knife.

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He allegedly threatened a woman before sexually assaulting her, then fled as she called for help.

The second incident allegedly occurred about 7am on Friday, when a man followed a woman outside a primary school on Langridge St before entering the school grounds.

Police allege he sexually assaulted the woman.

A woman was allegedly sexually assaulted after being followed near this primary school. Credit: 7NEWS

Police are investigating if the two incidents are linked.

A separate crime scene has also been established at a home on nearby Branton Rd after a resident reported a break-in overnight, with a number of items disturbed.

Victoria Police have increased patrols in the area, with officers and detectives conducting foot patrols while canvassing for CCTV footage and speaking to potential witnesses.

Investigators are urging anyone who was in the Whitsunday Dr or Langridge St areas about 11.30am on Thursday or 7am on Friday to check their CCTV or dashcam footage and contact Crime Stoppers if they have any information.