The share of middle-income households declined 90 per cent in 229 metro areas in the US between 2000 and 2014, a new report by the Pew Research Center, released yesterday showed.
The study revealed that the contraction was a national phenomenon, with overall around 51 per cent of US citizens living in middle class households in 2014, down from 55 per cent in 2000.
However, commentators point out that national statistics could sometimes obscure what was happening at a local level. For instance, in the late 2000s some places had been hit by the housing crash much harder than others.
When it came to the middle class, however, the trend held true in almost every metro area.
"The middle class is losing ground in communities all across the country," said Rakesh Kochhar. "In the North. In the South. In areas large and small."
He added the middle class was shrinking due to several reasons, among the main causes rising income inequality, driven by factors including globalisation, the decline of unions, the outsourcing of jobs and advancements in technology.
According to Pew, the middle class comprised people having incomes ranging from two-thirds to double the national median, based on household size.
The median was midway between the richest and poorest and by Pew's definition, a three-person household was middle class in 2014 if its annual income fell between $42,000 and $125,000.
Middle class adults now comprised less than half the population in such cities as New York, Los Angeles, Boston and Houston.
That sharp shift reflected a broader erosion that occurred from 2000 through 2014 with the middle class shrinking in nine out of every 10 metro areas, over the period, Pew found.
''The shrinking of the American middle class is a pervasive phenomenon,'' said Kochhar. ''It has increased the polarisation in incomes, '' AP reported.