General Motors Co will invest $336 million in a Detroit-area plant to produce its heavily anticipated Chevrolet Volt electric car beginning next year, the No. 1 U.S. automaker said on Monday.

Assembly of Volt prototype vehicles will begin in the spring at GM's Detroit-Hamtramck assembly plant, with the regular production scheduled for late 2010, GM said.

The plant currently employees about 1,200 workers, including 1,100 hourly workers represented by the United Auto Workers union.

GM said the investment brings the automaker's combined spending in Michigan related to the Chevy Volt plug-in car to $700 million.

(Reporting by Soyoung Kim, editing by Matthew Lewis)