Payday loan debts have rocketed by almost 50% in some areas - and thousands of people have taken out five or more at some point.
StepChange said the "frightening" figures showed why greater protection was needed for vulnerable customers.
It came as the government called an urgent summit to tackle the "widespread" problems found in the loan industry, which charges interest rates of up to 4,215%.
Lenders, ministers and charities will come together next week to discuss the loans, which have attracted severe criticism for their eye-watering interest rates.
The amount owed by people calling StepChange to ask for help with payday loans has spiralled in the past year.
In London, a typical 'problem' loan was £1,859 - up from £1,296 in a year.
Other 'hotspots' where sharp rises were reported were Cardiff, Liverpool, Leicester and Birmingham, where callers were struggling with an average debt of £1,637.
At the same time, more than 7,000 people who the charity StepChange had five or more payday loans - rocketing from just over 700 in 2009.
Delroy Cornialdi, of StepChange, said: “These figures offer a frightening insight into how certain communities appear particularly vulnerable to increasingly high levels of high-cost borrowing which could result in serious financial hardship."
On Thursday, the Office of Fair Trading (OFT) will decide whether it plans to refer payday lenders for a full-blown investigation by the Competition Commission.
The OFT previously uncovered evidence of "widespread irresponsible lending" and said the problems it had found were "deep-rooted", with lenders encouraging customers to roll over expensive loans and sink further into debt.