A horrifying discovery of a severed head has prompted a massive police lockdown in the heart of Edinburgh's old town, causing nearby pubs to be evacuated.

Eyewitnesses reported that the grim find was stumbled upon in Edinburgh's Cowgate area on Saturday night, although police cited a road traffic incident as the ongoing situation.

Disturbing images purportedly depicting the scene have circulated online, unleashing a torrent of "horrific" comments on social media questioning the authenticity of the photos. In a proactive response, forensic officers erected two tents at the crime site for extensive investigation.

The usually bustling nightlife was thrown into chaos after emergency services descended on the scene just past 8pm.

31-year-old Katie McLaughlin found herself amidst the chaos at Bannermans Bar, where she and her friends were abruptly informed that they needed to vacate the premises.

Hailing from Dumfries, Katie, who was on a weekend break in the Scottish capital, said: "There was a band playing at the back when an announcement was made that police were outside and had ordered them to shut the pub. We were in Bannermans having a drink and went to leave but a member of the staff stopped us." 

The staff directed the patrons towards an alternate exit, with Katie adding: "They then let us all leave by the back door but we were able to have a look down the street.

She continued, recalling her disbelief and initial thought that it was a Halloween prank: "He said police were outside and a severed head had been found in the Cowgate. I almost laughed because it's Halloween weekend and I thought it was a prank.

"We went to the bar where the staff said, no, it's real. They said that the police had ordered them to shut the pub. They then let us all leave by the back door but we were able to have a look down the street.

"I saw three police cars and five police officers and a small silver tent. The police were taping off the area. The whole area is sealed off. It just seems so surreal."

Another eyewitness recounted the sudden appearance of law enforcement: "Police just appeared and started putting tape up. Whatever it is, it looks pretty serious. There doesn't look to be any cars inside the cordon anyway."

Blair Street, Guthrie Street and Candlemaker Road have been sealed off as officers delve into the night’s unsettling incident.

Numerous establishments, including some gearing up for Halloween festivities, were instructed to shut their doors to facilitate the police operation.

Bachata Blues Edinburgh issued a statement, saying: "Following police instructions, all Cowgate venues are going to be closed tonight due to a major incident.

"All ways to enter Cowgate are cut off. Unfortunately, we have to cancel tonight's event as Mash House will remain closed all night, following police instructions.

"We will be back soon and hope to reschedule our night as soon as possible!"

Police were approached for a comment.