WASHINGTON—U.S. manufacturers have long grumbled about labor shortages, but the past year has proven particularly frustrating.

As the pandemic pushed millions out of work, most from service industries such as hotels and restaurants, many factories were pushed into overdrive by surging demand for everything from pickup trucks to plastic bags. And yet high jobless rates have not translated into workers flocking to open positions on assembly lines.

Earlier this month, the Labor Department said 916,000 jobs were created last month, the most since last August, including 53,000 manufacturing positions. That was the highest number of new factory jobs in six months.

The report’s manufacturing diffusion index, a measure of the breadth of hiring across some 75 goods-producing industries, registered one of its highest readings ever.

Manufacturing employment suffered a much less severe blow than service sector jobs last spring when COVID-19 first brought the economy effectively to a standstill. About one of every 10 factory jobs were eliminated in the shutdowns vs. roughly one of every six service jobs. Factory employment is 4 percent below pre-pandemic levels, a deficit of 515,000 jobs, versus 5.5 percent for overall U.S. employment, with a total shortfall from February 2020 of 8.4 million positions.

Other indicators also point to a tight labor market at factories. Earlier this month, the Institute for Supply Management said its index for national factory activity jumped to its highest reading in 37 years in March, with its gauge of manufacturing employment rising to its highest level since February 2018.