WASHINGTON — U.S. job openings fell to the lowest level in more than five years, another sign that the American labor market remains sluggish.

The Labor Department reported Tuesday that vacancies fell to 6.5 million in December — from 6.9 million in November and the fewest since September 2020. Layoffs rose slightly. The number of people quitting their jobs — which shows confidence in their prospects — was basically unchanged at 3.2 million.

December openings came in lower than economists had forecast.

The economy is in a puzzling place. Growth is strong: Gross domestic product — the nation’s output of goods and services — advanced from July through September at the fastest pace in two years. But the job market is sluggish: Employers have added just 28,000 jobs a month since March. In the 2021-2023 hiring boom that followed COVID-19 lockdowns, by contrast, they were creating 400,000 jobs a month.

Economists are trying to figure out if hiring will accelerate to catch up to strong growth or if growth will slow to reflect a weak labor market or if advances in artificial intelligence and automation mean that the economy can roar ahead without creating many jobs.