Toyota Motor and Mazda Motor are expected to announce on Wednesday that they have chosen a location in northern Alabama, near Huntsville, for the $1.6 billion car plant the Japanese automakers are planning to build together, according to a person familiar with the companies’ plans.

Details of the assembly plant, which is expected to employ about 4,000 people and open by 2021, will be disclosed at a news conference with state and local officials in Montgomery, this person said.

A Toyota spokeswoman, Amanda Roark, declined to comment.

Toyota already operates four auto assembly plants in the United States, in Kentucky, Indiana, Mississippi and Texas. It also has two in Ontario and a small truck plant in Mexico. Mazda has a single North American plant in Salamanca, Mexico.

The location of the plant was first reported by Reuters.

The new Alabama plant, when completed, is expected to assemble a new version of the Toyota Corolla compact car. Mazda has not yet said which automobile the joint plant will produce. The factory, which will have the capacity to make up to 300,000 cars a year, is part of an initiative by Toyota to invest $10 billion in the United States over the next five years.