WASHINGTON (AFP) - The US jobs machine shifted into a higher gear in September, pushing the unemployment rate down to 5.9 per cent, the lowest level in six years.

In a boost for President Barack Obama a month before midterm congressional elections, the Labour Department reported Friday that the economy pumped out 248,000 net new positions last month.

Together with upward revisions from previous months, this eased concerns about a late-summer slump in job creation.

The solid run so far this year - an average of 227,000 jobs each month - brought the number of officially unemployed down to 9.3 million, the lowest level since July 2008.

But the data also showed continued weakness in wages, and still-large numbers of long-term unemployed, part-time workers and labour market dropouts.

That could challenge Mr Obama's bid to prove that his stewardship over the economy has served Americans well, ahead of the November mid-term congressional elections.

Mr Obama's Democrats are battling to prevent Republicans from seizing control of both houses of Congress, and the President hit the campaign trail on Thursday to promote his economic record.

In a speech at Northwestern University, he pointed out that in the aftermath of the 2008-2009 recession, the United States "has put more people back to work than Europe, Japan, and every other advanced economy combined."

"It is indisputable that our economy is stronger today than when I took office. By every economic measure, we are better off now than we were when I took office," he argued.

The September jobs market data underscored those gains.

Job creation was strongest in the restaurant industry, health care, food and beverage stores, and administrative services, with also modest additions in construction and government hiring.

But weaknesses persist. The number of those who have dropped out of the labor market - a volatile figure month-to-month - rose by 315,000, almost as much as the fall in the number of unemployed.

The civilian labour force participation rate fell a tick to a new low of 62.7 per cent, far below the 66 per cent level prior to the severe 2008-2009 recession.

The number of involuntary part-time workers was little-changed in September at 7.1 million, and wages were down slightly for the month.

The unemployment rate has fallen steadily from the peak of 10 per cent in October 2009, nine months after Mr Obama took office.

But average weekly wages have risen by just over 2 per cent a year since then, barely staying ahead of inflation, adding to the feeling among many Americans that things have not improved.

"Policy makers will certainly be worried by the lack of wage growth," said Chris Williamson of economic consultancy Markit.

"Without substantially higher wage growth, the fear is that households will pull back on consumption if interest rates and borrowing costs start rising, snuffling out the wider economic recovery."

The September jobs data also adds little fresh pressure on the Federal Reserve, which has been focused on cutting joblessness, to move more aggressively to tighten monetary policy from the current easy-money stance.

Fed chair Janet Yellen has argued for much of the year that significant slack in the labor market gives the central bank more time before it has to raise its benchmark fed funds interest rate up from the zero-level where it has been since late 2008.

So far the Fed has signalled it expects an initial rate hike in the second half of 2015.

But analysts said that if the current pace of job creation holds up, and if wages pick up, that could be advanced.

Economist Harm Bandholz of UniCredit said he expects wage gains "are about to gain some momentum" and the Fed could also shift gears "faster than currently anticipated by most financial market participants."