Two masked men brandishing hammers demanded money from a shop in Weston-super-Mare but left empty-handed when staff fought them off.
They entered the Premier convenience store in Mead Vale but were forced to leave after a struggle with the shopkeeper and an employee.
The attempted robbery happened at 0615 BST on Monday.
Detectives in the town are also investigating two other incidents which happened earlier the same morning.
Both of the offenders are described as being white.
Police appeal
One was of medium build and the taller of the two. He wore a blue coat with black panels, blue jeans and white trainers.
The second was shorter and of slighter build. He wore a white hooded top, blue jeans and black trainers.
In the first of the other incidents two men were seen near Banwell News in West Street, Banwell at 0510 BST. They made off when challenged.
The other incident was at 0550 BST when two men were seen acting suspiciously behind Martins Newsagent, Queensway, Worle.
DI Leanne Pook of Weston CID said: "We are obviously looking into all these incidents. I would appeal for anyone who recognises the description of these two men, or who has any other information.
"I would urge people working in or living near newsagents or convenience stores to be on the lookout for anyone behaving suspiciously and to call police immediately."
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