Toyota's Alabama engine plant has opened a second V6 engine line, the fifth significant investment since the plant factory opened to make V8s 11 years ago.

The plant has also just produced its three millionth engine.

Jim Bolte, president of Toyota Alabama, said: "Our new V6 is particularly monumental because we are now the only Toyota engine plant in the world with four separate production lines."

Toyota's total spend at the Alabama plant will exceed US$850m by July 2015 when the current $150m machining project is completed. Last year, Alabama produced more than 540,000 engines, a plant record. Maximum engine capacity is nearly 750,000.

The plant is the only Toyota factory to produce I4, V6 and V8 engines under one roof; it produces engines for seven North American-built models: Camry; Highlander; RAV4; Sequoia; Tacoma; Tundra; and Venza.