Cycle thieves have struck 77 times in the centre of Leicester in the past month.
The spate of bike thefts has taken place in Castle ward, which includes the city centre, parts of the two university campuses and Clarendon Park.
Police warned riders to take basic security measures to help combat the surge in thefts.
They are also staging extra patrols to catch the thieves and have arrested a number of suspects.
Tim Hudson, co-director of Future Cycles, in St Martin's Square, in the city centre, warned the true scale of the problem could be even worse.
He said: "I would guess half of the people who have their bikes stolen don't report it to the police, so it's almost certainly a lot more than 77 in the past month.
"We point out to people that some of the locks available could be cut with a pair of scissors and there are people walking around the city with bolt croppers up their sleeves.
"The punishment for stealing a bike is pretty low, especially compared to that for stealing a car."
Kelvin Morris, 34, of Clarendon Park, Leicester, had a bike stolen in the city centre.
He said: "That was my fault, because I hadn't put the lock on it.
"I have a good-quality lock now and use it every time.
"I also chain my bike up in a busy place, even if it's bit of a walk from where I'm going.
"My bike cost more than £500 so I'm not going to let a thief get his hands on it.
"I'd also recommend people spend at least £20 or £30 on a good-quality lock."
Sgt Jim Smallman, of city centre police, said officers were patrolling areas where thieves have been active. He said before the current spate of thefts, the number of such offences had been lower than it was last year.
In July, August and September, the average number of bike thefts was 45 a month. That was down on 63 a month for the same period the previous year.
Police advised cyclists to chain their bikes to cycle racks or other substantial fixtures in well-lit and busy areas and to etch their postcode on the frame.
They urged people to use D-locks, which are strong and heavy and difficult to cut through.
Sgt Smallman said: "We've run initiatives to tackle the thefts and we have given away D-locks in various parts of the city.
"We're not aware of any bikes which were fitted with D-locks being stolen.
"Now, we're looking at running further initiatives and we're reiterating the need for people to get an appropriate lock as a way of reducing the chances of their cycles being stolen."
Sgt Smallman urged people to contact police if they had information about the underground trade in stolen bikes.
Cycles can be left for £1 a day at the Bike Park, in Town Hall Square. It is run by Leicester City Council and Future Cycles.
Cyclists can register their bikes on the UK National Property Register at:
www.immobilise.com
A 26-year-old man will appear before Leicester magistrates next month charged with being in possession of a cycle which had been stolen in Newarke Close, Leicester, last week.
