When Jesus came preaching the Kingdom of God, he said it was "at hand" and commanded us to repent and believe the good news about the Kingdom (Mark 1:14-15; Matthew 4:17). The Greek word translated "at hand" is engizo. It means to draw near to something. It does not imply that something has actually come, rather that it is close.
The Bible in Basic English, the New International Version and Today's English Version recognize this distinction, translating the phrase in Mark 1:15 as "the kingdom of God is near."
Other translations, including the New Revised Standard Version, Modern King James Version and Green's Literal Translation, state that this Kingdom "draws near" or "has come near." They make it clear that the Kingdom of God has not arrived, but that it is near.
What Jesus was saying had to do with the message of the Kingdom, as well as the availability of Himself as the King of that Kingdom. The Kingdom in that sense was very near to them, even though it would not arrive in the literal way God had revealed it to Daniel for quite some time.
Jesus Christ was the personification of the message of the Kingdom. He was the Ruler, the King of the Kingdom. He was its representative, the One through whom humanity would be able to enter the Kingdom.
His message was that people should repent, believe the good news that He brought and put that message into action, changing their lives to reflect their belief and commitment.