NEW YORK, Jan 20 (Reuters) - McDonald"s Corp (MCD.N) said on Thursday it will expand its U.S. test of a plant-based burger it created with vegan meat maker Beyond Meat Inc to about 600 locations next month. The restaurants - in San Francisco, California and Dallas-Forth Worth, Texas - will sell the so-called "McPlant" burger starting Feb. 14 for as long as supplies last in order to "help us understand customer demand," the Chicago-based chain said in a post on its website. Shares of Beyond Meat, which makes the McPlant patty from peas, rice and potatoes, were up more than 5% at midday. McDonald"s initially tested the burger in eight U.S. locations in November. read more In December, two Wall Street analysts forecast a major U.S. expansion of the McPlant. read more One of those analysts, BTIG"s Peter Saleh, said on Thursday that the expanded test "moves the product one step closer to a national launch, which could be worth several hundred million dollars" to Beyond Meat.