Two shops, a garage and a home were targeted in four armed raids in Norfolk.
A gun, knives and a hammer were used to threaten victims in the robberies in Norwich, King's Lynn and Downham Market.
Detectives are continuing to investigate the raids and are linking the two in Norwich.
They are separately linking the two West Norfolk robberies.
A man wearing a skull mask threatened a shopkeeper with a gun in Larkman Lane, Norwich.
The manager grabbed a broom handle to defend himself and the robber fled empty-handed.
Less than two hours later three men threatened home owners in another part of the city.
Yesterday morning an armed raider stole items from a Lynn shop and then a car was stolen at knifepoint in Downham Market.
A man was later arrested in London in connection with the West Norfolk raids.
'When I saw the gun I just panicked'
Police are linking the attempted robbery of the Kwiksave store on Larkman Lane with a home invasion two hours earlier, when three men forced their way into a house and stole a wallet and handbag.
Around 9.15pm on Wednesday, a man clad in a skull mask and wearing gloves entered the Kwiksave store, brandished what appears to be a gun and told the shopkeeper to empty the till.
Manager of the store Rajiharan Arulampalam, known as Raj, was alone in the shop at the time and grabbed a broom handle to defend himself.
'When I saw the gun I just panicked,' he said. 'He came in and started pointing the gun at me and asked me to open the till. 'I just said 'ok, wait', and tried to get my phone from where it was on charge to call the police.'
When the attempted robber clambered over the counter, Mr Arulampalam ran through the stock room and out into the street, in a bid to lock the man inside the store until police arrived.
'I ran to the back of the store and went outside, as I spoke to police on the phone,' he said.
'I didn't realise if it was a real gun or a toy gun but I didn't want to take the risk.'
The would-be robber tried to open the till and failed, leaving empty handed.
The till had been empty at the time anyway, said Mr Arulampalam.
'I would have tried to lock him in the shop if there had been other people around,' he added.
'I just wanted to grab my phone so I grabbed the broom stick to threaten him until I could get away. The stick was too big to reach over the counter so I might cut it down in case this happens next time.'
Less than two hours earlier, a man fitting the same description and wearing a skull mask had been involved in an aggravated burglary on Theobold Road, the other side of the city.
At around 7.30pm the occupants of the address answered the door to three men who pushed their way in and demanded money.
One of the men was armed with what is being described as a gun while another man was carrying what is believed to have been a hammer.
One man inside the house was assaulted with the hammer, but his injuries are not believed to be serious. A handbag and a wallet were stolen before the three men left the property on foot.
'I didn't have time to feel scared'
Officers were called to the JD Sports store in Lynn High Street at around 9.55am yesterday after a man entered the store and threatened a female staff member with a knife before he stole trainers, gloves and clothing.
Shortly before 10.30am officers were called to Lynn Road in Downham Market after a man was threatend with a knife at a petrol station, by a man who drove off with his care.
The red Vauxhall Corsa, registration RA12 TGU, was last seen heading south on the A10 towards Ely.
One man, who has worked at the Jet petrol station on Low Road for 19 years, said it was the first time anything like this had happened at the business.
'It was all over in two minutes,' he said. 'I didn't have time to feel scared. 'A man was dropped off by a taxi and went up to a customer with a knife. There was some arguing between the two men but then I saw the customer take his house key off the car keys and the man got in the car and drove it away. The customer came in, shaken and I called the police.'
Mayor of Downham Market, David Sharman said: 'I am horrified, it's so unsual for Downham Market to have anything like this, to my knowledge it's never happened in Downham before. I hope we don't have any repetition of it.'
Jonathan Toye runs West Norfolk Disability Information Service (WNDIS) and lives opposite the Jet petrol station said: 'It's usually a very quiet and peaceful road, the people who work in the garage are lovely, it's not that sort of road.'
No one was hurt in either incident.
Police later said a man in his 20s had been arrested in London in connection with the incidents and would be brought back to Norfolk for questioning.
• Anyone with information should contact Norwich CID on 101 or King's Lynn CID on 101.
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