What was the moment both China and North Korea made public that a large number of ‘volunteers’ from China were fighting on the side of North Korea?

What was the moment both China and North Korea made public that a large number of ‘volunteers’ from China were fighting on the side of North Korea?
Did Communist China consider it important to make clear at an early moment that these soldiers were not fighting as an act of war by the ‘Peoples Republic of Chima’, but only as ‘volunteers’?

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