Cars have been stolen by two violent gangs during late-night attacks in ritzy bayside suburbs.
The spree started about 1.15am on Thursday in Brighton, when a 42-year-old woman stopped her red Toyota Corolla on Young Street.
She was confronted by two men who assaulted her before taking her car and some jewellery.
The men fled in the Corolla, which collided with a Holden Statesman at the intersection of Glen Huntly Road and St Kilda Street in Elwood a few minutes later.
The driver of the Holden, a 55-year-old Eltham woman, was uninjured, but her car was wrecked.
The men, who were of African appearance, fled in a dark sedan. It is unclear whether this sedan was also stolen, a police spokeswoman said.
Box Hill Embona task force detectives, who investigate armed robberies, are appealing for information about the attack.
In a separate attack about 4am on Wednesday, a family were woken in their Port Melbourne home by three men.
One of the intruders struck a 53-year-old man who lived in the house with a blunt instrument, leaving him with a cut to the head.
Police said the trio then stole mobile phones and the keys to the family's 2014 Mercedes sedan before fleeing the Ross Street property.
The men were last seen travelling east on Ross Street in the car, which has the registration VAS 469.
No description of the attackers has been released.
Southern Metro detectives are investigating.
Anybody with information about either incident is urged to contact Crime Stoppers on 1800 333 000 or via crimestoppers.com.au.