Are there eyewitness accounts of Jesus Christ written during (or closely after) his lifetime? In recent times, it has come to my understanding, that the New Testament was written in its entirety only after Jesus Christ has died.

I ask for in the search of documents which date to Jesus' lifetime(or closely after) and which give us account from people who have seen the Lord with their own eyes.
Are there eyewitness accounts of Jesus Christ written during his lifetime?

The short answer is no.

The entire New Testament was written well after the crucifixion of Our Lord Jesus Christ.

Even the first-century Romano-Jewish scholar, historian and hagiographer Titus Flavius Josephus, commonly known as Josephus references Jesus in the year 93 A.D. Again, this is well after Jesus died.


  About this time there lived Jesus, a wise man, if indeed one ought to call him a man.  For he was one who performed surprising deeds and was a teacher of such people as accept the truth gladly. He won over many Jews and many of the Greeks. He was the Messiah. And when, upon the accusation of the principal men among us, Pilate had condemned him to a cross, those who had  first come to love him did not cease.  He appeared to them spending a third day restored to life, for the prophets of God had foretold these things and a thousand other marvels about him.  And the tribe of the Christians, so called after him, has still to this day not disappeared. -  Jewish Antiquities, 18.3.3 §63