(Adds CEO interview, share price reaction, analyst) COPENHAGEN, Aug 11 (Reuters) - Vestas cut its 2021 outlook on Wednesday in response to higher costs and supply constraints, sending its shares down, as the world’s biggest wind turbine maker reported second-quarter operating profits that fell short of forecasts. Demand for Vestas’ wind turbines, seen as crucial to curb global warming, remains healthy but has been affected by constraints in the freight market related to the impact of COVID-19 which have conspired to drive global supply chains towards breaking point. “This is not business as usual when you have a transport (cost) that in some parts of the world increases with potentially 800 to a thousand percent,” chief executive Henrik Andersen told Reuters. “And it’s not only the cost of transporting ... but it is also if you can actually rely that the goods are arriving on the day,” he added. Andersen said higher raw material prices had also driven up the cost for most of the components used in Vestas’ wind turbines. The company now expects full-year revenue of 15.5 billion to 16.5 billion euros, down from a previous forecast of 16-17 billion euros. It also lowered expectations to its operating profit margin to 5-7% from previously 6% to 8% - a far cry from its long-term target of a 10% margin. Its shares fell 7% at market open but reversed some losses and were down around 1.4% at 0750 GMT. Analysts said the cut to Vestas’s outlook was unsurprising. “We have heard and seen the same from GE and Siemens Gamesa so this should not come as a major surprise,” said Sydbank analyst Jacob Pedersen. Despite the challenges, Vestas’ operating margin still remains well above that of its main rival Siemens Gamesa , which reported a negative margin of 5.6% in the same period and last month cut its profit margin outlook for the year to between -1% and 0%. Vestas reported second-quarter operating profit before special items of 101 million euros ($118.32 million), below the 170 million euros expected by analysts in a poll. Reporting by Stine Jacobsen; editing by Jason Neely, Louise Heavens and Jane Merriman Our Standards: The Thomson Reuters Trust Principles.