Two armed men dressed in Royal Mail uniforms raided a post office in Greater Manchester.
One of the men, who was carrying a handgun, broke into the back of Cheadle post office in Wilmslow Road, Stockport at about 1000 BST on Thursday.
He stole money from the tills and stashed it in a dark sports bag. He then fled out the back, where police believe his accomplice was on guard.
They threatened a member of staff who tried to stop them as they fled.
The robbers then jumped over a wall and made off in the direction of Warren Avenue.
Det Sgt Graham Lynn, of Greater Manchester Police, said: "We are keen to hear from anyone that has information that may help us identify these two men.
"No-one was injured during the robbery but the fact these two men were carrying a gun understandably left the staff and customers terrified.
"The pair made off towards Warren Avenue where there is an office block at its junction with Gatley Road, and it is possible they may have got into a car around here to make their getaway.
"If anyone saw these men or saw any suspicious vehicles parked up, please get in touch with us as your information could be vital to our investigation."