Three men were robbed in three separate incidents in Preston in the early hours of Sunday morning.
The series of robberies happened between 00.30am and 03.45am in the Ripon Street, Shelley Roadd and Villiers Street areas of Preston.
Lancashire Police said all three of the victims are male.
Officers said in each case two men approached the victims and demanded property from them.
Details of what was taken have not been released.
The offenders were white men wearing dark coloured clothing.
In a statement Preston Police said: “These incidents were extremely frightening for the victims to have gone through and we would appeal for anyone who may have seen anything suspicious to get in touch with us.
“It may be that people were out returning home themselves and may have seen something that could assist in identifying the persons responsible.”
Anyone with information should contact police on 101 quoting log number LC-20150419-0273 or contact Crimestoppers on 0800 555 111 or online at crimestoppers.org