The United States will have to rely in part on immigrants to fill jobs created thanks to President Donald Trump's tax reform plan announced this week, the head of global staffing company Manpower said.

Trump proposed on Wednesday the biggest U.S. tax overhaul in three decades, aimed at helping working people with tax cuts and creating jobs.

"Immigration will have to support the increased jobs growth because right now the labour markets are extremely tight as they are," Manpower Chief Executive Jonas Prising told Reuters in an interview in Paris.

Though active in 80 countries, the United States is the Milwaukee-based recruiter's biggest market after France, according to Thomson Reuters data.

Although the U.S. unemployment rate has been running in recent months at a 10-year low around 4.4 percent, Prising said there was scope to absorb extra workers into the labour market.

With the labour force participation rate at close to a 40-year low, the pool of available workers could in part be increased by skilling up people currently sitting on the sidelines but also through immigration, Prising said.

"The issue is going to be where are those people going to come from," he said.

"That's where some of the rhetoric and some of the thoughts about immigration and how we think about our talent pool are frankly going to be counterproductive," he added.

An increased demand for workers from abroad could sit at odds with Trump's plans to clamp down on immigration, which he hopes to slash by building a wall on the border with Mexico.