That construction met the requirements for Boeing to qualify for subsidies from the state of Missouri that could reach $229 million over 18 years. Boeing would have to increase its St. Louis workforce by 2,000 jobs to qualify for the full subsidy. The unusual agreement allows Boeing to reap smaller payments if it simply keeps employment over 12,500.

The 777X is a long-haul, double-aisle airliner designed to carry up to 400 passengers while using less fuel than the competition.

Production of 777X wing edge and tail parts is expected to begin at the plant in early 2017, the company said.

Boeing had 306 orders for the 777X through September. The 777X replaces the highly successful 777, introduced in 1995.

The ribbon-cutting Thursday morning included Boeing employees and Gov. Jay Nixon, a Democrat, who helped push for incentives for the plant expansion.

Boeing Defense, Space & Security division is based in Hazelwood and the company currently has about 15,000 workers in the St. Louis area.