The S&P 500 and Nasdaq again finished at fresh records on Wednesday, extending a positive run following mixed economic data in a quiet holiday-shortened session.

US private-sector hiring came in a bit below expectations for June, while a report from the Institute for Supply Management showed a surprise contraction in services industry activity.

Markets are looking ahead to Friday's jobs report, said Art Hogan of B Riley Wealth Management, adding that the labour market seems to be "normalising but not collapsing."

Hogan described trading volumes as extremely low ahead of the July 4th holiday.

The S&P 500 gained 0.5 percent to 5,537, while the Nasdaq jumped 0.9 percent to 18,188.

The Dow Jones meanwhile lost 0.1 percent at 39,308.

Among individual companies, Southwest Airlines advanced 1.6 percent after announcing a shareholder rights plan designed to prevent Elliott Investment Management from gaining a controlling stake in the carrier.

Paramount Global jumped 6.9 percent following reports that it reached a deal to be bought by movie studio Skydance after earlier breaking off the talks.

Constellation Brands dropped 3.8 percent after reporting a 22 percent jump in quarterly profits to US$877 million behind strong beer sales. However, net sales in wine and spirits fell. (AFP)