The first incident took place on Tuesday 3 November between 10 and 10.15pm at Guildhall Square. Two men were threatened with a knife by a group of men who then stole a designer coat and air pods from the first man and money from the second man.
In the second incident, at 10.50pm on the same evening a man has been threatened with a knife by a group of six men on Commercial Road but nothing was stolen.
At 11pm that night, a man had his wallet, which contained a bank card that was later used, stolen at knifepoint by six men on Canal Walk. The suspects also stole a phone from a friend of the man who was with him at the time.
On Wednesday 4 November at approximately 7pm a man was threatened with a knife by four men and had his phone stolen on Commercial Road.
Later that evening at around 10.40pm, six men approached a man on Isambard Brunel Road and stole his jacket, electric scooter and wallet, which contained various bank cards.
No one was harmed in either of the incidents.
Three 17-year-old men, two 18-year-old men and a 19-year-old man from Portsmouth have been arrested on suspicion of knifepoint robbery and robbery in connection with all six incidents.
The arrests come as officers from the Portsmouth Neighbourhoods High Harm Team intensify their patrols across the city in relation to #OpSceptre; a national week of action targeting knife crime.
Inspector Scott Johnson said: “We know the harm that knife crime can cause to our communities, particularly our young people, and that it is often linked to drug-related harm, robbery and domestics, with fear of crime often cited as a reason for carrying a weapon.
“We care about young people and would always prefer to prevent crime rather than detect it as this means something has happened to someone. We never want to see a young person hurt or in trouble if it can be prevented. We will always help if someone feels threatened, frightened or they think they are at risk of harm.
“Pre-planned police activity will continue to take place this week as part of our work to reduce knife crime and we will take robust action to help protect people from harm