U.S. private businesses added a robust 253,000 jobs in May, a private survey found, a sign that employers expect economic growth to keep plowing ahead.

Payroll processor ADP said Thursday that the hiring primarily came from companies with fewer than 500 employees_which accounted for more than 75 percent of the jobs added last month. Total hiring is up from 174,000 jobs in April and nearly matched the 255,000 jobs added in March.

The strong gains all point to a falling unemployment rate. This is because the hiring exceeds the roughly 80,000 people who come into the job market each month, said Mark Zandi, chief economist at Moody's Analytics. With hiring at the current pace, companies are choosing among a shallower pool of jobseekers_which may cause many firms to raise pay in order to attract talented workers.

"Labor shortages are quickly becoming businesses' number one problem_and that problem is only going to get worse," said Zandi, who expects that the government's 4.4 percent unemployment rate could soon fall below 4 percent.

The ADP jobs figure is much higher than economists' forecasts for the government's jobs report, to be released Friday. Analysts predict that report will show 176,000 jobs were added, according to data provider FactSet.

The ADP covers only private businesses and often diverges from official figures.

The job gains in the ADP survey were led by big increases in construction, education and health, and professional and business services, which includes high-paying fields such as accounting and engineering. Construction hired 37,000 workers and manufacturers 8,000. Professional and business services added 88,000 jobs, while the education and health sector contributed 54,000 jobs.

But the leisure and hospitality sector_usually a major source of job gains in the government report_shed 11,000 workers last month in the ADP survey.