One police source said the man had an “unconventional” weapon when he targeted the NatWest branch in George Street, but a police spokesman said today that no weapon had been seen or used.
The suspect struck at the bank at around 3.50pm yesterday, threatening staff before making off with the money.
Last night, the bank was sealed off with police tape while forensics officers studied the scene.
Two officers were stationed at the door while detectives inside took photographs of the branch interior.
Workers in neighbouring buildings were quizzed by police but most appeared to be oblivious to the drama.
A staff member at the Amarone Ristorante, next door to the bank, said: “All we know is that the police came and asked if anyone had run into the restaurant, and we said ‘no’.”
Most of the staff leaving the building refused to talk about their ordeal.
One young woman simply said: “I can’t say anything. No-one will speak to you.”
Another worker claimed not to have heard anything in the main bank as she had been working in the back of the building.
She said: “I was in the back with someone. I never saw a thing.”
The man is described as being in his late 20s to early 30s, with dark hair. He was wearing a dark grey jacket and possibly dark jeans.
He was carrying a cream coloured bag with black patches on it.
A Lothian and Borders Police spokesperson said: “Police responded to an incident at a bank on George Street, Edinburgh, at around 3.50pm after a four-figure sum of cash was stolen.
“The man threatened staff and obtained the money from them before making off from the address.
“Inquiries are currently at an early stage and police are appealing for any information to trace the suspect.”
Onlookers took to social networking sites to describe the scene as the police arrived and cordoned off the bank.
One Twitter user, PedroWolf, described “pandemonium” on George Street while Philip Kelly tweeted: “Police tape and two officers on watch outside Natwest, George Street. Things really getting that bad?”