Financial inequality became even wider in the United States last year, with average income for the top 1 per cent of households surging 7.7 per cent to $1.36 million.

Income for the richest sliver rose twice as fast as it did for the remaining 99 per cent of households, according to an updated analysis of tax data by Emmanuel Saez, an economics professor at the University of California, Berkeley.

Still, the incomes of households outside the top 1 per cent appear finally to be recovering from the Great Recession, which officially ended seven years ago.

National problem: Wealthy presidential candidates Donald Trump and Hillary Clinton are tasked with pitching ways to combat the widening gap between the haves and the have-nots

After accounting for inflation, their average income rose 3.9 per cent last year to $48,768 — the strongest annual gain since 1998.

Contrast that with the period from 2008 to 2011, when the economy remained in a rut and inflation-adjusted income for the bottom 99 per cent of households was falling.

'It is indeed the best growth year for the bottom 90 per cent and bottom 99 per cent since the late 1990s,' Saez said.

'At the same time, top incomes grow even faster, leading to a further widening of inequality, which continues an alarming trend.'

Income inequality has been a rallying cry of the 2016 election, with more Americans turning fearful and angry about a shrinking middle class.

Donald Trump has pledged to restore prosperity by ripping up trade deals and using tariffs to return manufacturing jobs from overseas.

Hillary Clinton has backed a debt-free college option and higher minimum wages to help the middle class.

The current gap between the uber-wealthy and the rest of Americans is at its largest since the 1920s - when industrialists like the Rockefellers and Vanderbilts lived like gods

Much of the debate has been fueled by research conducted over the years by Saez and his collaborator Thomas Piketty.

The IRS data reviewed by Saez shows that income growth last year was greatest among the super-wealthy — the top 0.1 per cent of households.

Their incomes climbed nearly 9 per cent to an average of $6.75 million.