US consumer confidence dipped in April, with fewer Americans seeing prospects of a pick-up in economic growth in the coming months, the US Conference Board has said.

The Board's consumer confidence index fell to 94.2 from 96.1 in March as dimmer future expectations outweighed an improved view of current conditions.

The decline in sentiment was unexpected, with analysts forecasting a slight improvement this month.

The report came as the Federal Reserve opens a two-day policy meeting widely expected to leave ultra-low interest rates unchanged amid signs of slowing US economic growth and modest consumer spending.

"Consumer confidence continued on its sideways path, posting a slight decline in April, following a modest gain in March," said Lynn Franco, director of economic indicators at The Conference Board, in a statement.

"Consumers' assessment of current conditions improved, suggesting no slowing in economic growth.

However, their expectations regarding the short term have moderated, suggesting they do not foresee any pick-up in momentum," she said.

The number of survey respondents viewing the present situation as "normal" rose and those believing jobs "hard to get" fell, helping to push the present situation sub-index up roughly two points to 116.4.

But the outlook for the six months ahead dropped almost twice as much, to 79.3.

The survey found 11.0% of consumers expected business conditions would deteriorate, compared with 9.5% in March.

They also showed less confidence in jobs availability in the future.

Ian Shepherdson of Pantheon Macroeconomics said the report signals a lagged reaction to the decline in stock prices in the first two months of the year.

"Over the next couple of months, we expect a clear rebound in consumers' sentiment and spending after the subdued first quarter," Shepherdson said.

The first official estimate of first-quarter gross domestic product will be reported on Thursday by the Commerce Department.

Analysts expect GDP grew at a modest 0.9% in the January-March period, slowing from a 1.4% rate in the 2015 fourth quarter.