Part of Carron Place in Springburn, Glasgow, was sealed off overnight after shots were fired in the common close at 5.35pm.
The emergency services were attended but there were no injured people at the scene.
Officers are appealing for witnesses to come forward.
Detective Inspector John Morrison said: “This type of reckless and violent behaviour will not be tolerated and it is absolutely imperative that we trace the individuals involved.
“Many people will have been enjoying Christmas Day within their homes at the time of the incident and I would ask anyone who heard or saw anything suspicious to please get in touch.
“From inquiries carried out so far, it is understood that two men were seen leaving the block of flats immediately after the incident and it is vital that we trace them.
“We are still working to establish a motive for this incident however at this time there is nothing to suggest that it is linked to any particular organised crime group.”
Inspector Craig Walker from Maryhill Police Station said: “This incident will understandably be concerning for the local community and I would like to reassure people that we are doing everything we can to trace the individuals responsible.
“There will also be additional patrols in the area to provide reassurance and if anyone has any concerns please feel free to approach them.”
Police have increased patrols in the area while investigations take place.
Officers did not know what type of firearm had been used.
Anyone with information is asked call 101 or Crimestoppers anonymously on 0800 555 111.