It was a big upswing from the 505,000 gain in November and nearly double the increase economists had been expecting, but the hit from the fast-spreading Omicron variant may still be ahead.

The data offers a preview of the government employment report due out Friday, but ADP can be far out of line with the official figures.

Economists are projecting the jobs report will show the US economy added 440,000 jobs in the final month of the year, nearly twice the disappointing November result.

ADP said service firms, including restaurants and hotels that were the hardest hit by the Covid-19 pandemic, added 669,000 workers last month, while goods-producing companies hired 138,000.

"December's job market strengthened as the fallout from the Delta variant faded and Omicron's impact had yet to be seen," ADP chief economist Nela Richardson said.

"Job gains were broad-based, as goods producers added the strongest reading of the year," Richardson said.

ADP said private hiring in the fourth quarter averaged 625,000, topping the 514,000 average for the year.

But "while job gains eclipsed 6 million in 2021, private sector payrolls are still nearly 4 million jobs short of pre-Covid-19 levels," Richardson said.