Knifepoint robbers have targeted four victims in just three-and-a-half hours during a spate of attacks.
The male victims were all confronted in Colchester, Essex, between 23:00 BST on Friday and 02:30 on Saturday.
Essex Police said extra patrols would be made in The Hythe and New Town over the weekend.
The force said the crimes were being linked and that it was "working with the victims in each incident to identify the suspects".
The first victim managed to flee unscathed after being surrounded by a group of up to 15 men, one armed with a knife, in Hickory Avenue at 23:00.
A man then had his wallet and phone stolen after he was approached by two men who pulled out a knife. The pair were with two women at Hythe Station at 01:30.
Forty-five minutes later, a gang of up to six males stole a man's phone at knifepoint in Winnock Road, before a fourth man managed to push a would-be robber away when he was threatened with a knife at 02:30 in Hythe Hill.
Det Ch Insp Leighton Hammett said: "We have a zero tolerance stance on this type of behaviour and these incidents are not acceptable."