Massachusetts and New Hampshire have the strongest economies in New England, but experts say continued growth depends on immigration.

That was one message delivered during an economic outlook conference hosted by the New England Economic Partnership at the Federal Reserve Bank of Boston on Tuesday.

"We're highly dependent on growing our labor force by net foreign immigration, so anything that slows that could hurt our economy," Northeastern University's Alan Clayton-Matthews said during the conference.

Gregory Bird, of the New Hampshire Center for Public Policy Studies, reported that New Hampshire and Massachusetts are projected to have the highest employment growth in New England. At 2.9 percent, Massachusetts is already tied with North Dakota for the third-lowest unemployment rate in the country. New Hampshire and South Dakota are tied for lowest, at 2.7 percent.

But the shortage of skilled labor is worse in New England than in the rest of the country, and experts say that shortage is slowing growth.

Because the region is already at full employment, economists say there aren't a lot of people here to fill the available skilled jobs.

Clayton-Matthews projects that the growth of the labor force will slow as baby boomers retire, and that will slow the economy. He says the aging of the workforce is tempered by millennials who are moving to Massachusetts, but people over 30 are moving out.

"The key for Massachusetts going forward is labor force and population growth," Clayton-Matthews said.

Clayton-Matthews expects that under Republican leadership in Washington, Massachusetts will benefit from increased federal spending and lower taxes.