The 206cm giant is playing just his eighth Test and removed Australia allrounder Cameron Green in his first over of the morning at the Gabba on day two. He followed that up with top-scorer Travis Head in the same over to make it a double.
"I saw him when he was a 12-year-old when he used to come down to the nets and bowl to the South African team," Morkel told AAP.
"From a very young age there was something special about him. To see how he's progressed to playing for South Africa now is amazing.
"He is over two metres tall, bowling a good length and a good pace and that is a difficult for batters to face. He has everything going for him and is a fantastic addition and find for this bowling unit after we lost a lot of experience with Vernon Philander, myself and Dale Steyn."
The 22-year-old finished with 3-32 from his nine first innings overs in his first Test on Australian soil.
He already has 40 Test wickets at an average of 18.Â
With his height, Jansen is ideally suited to pitches in Australia. He doesn't need to fall into the trap of bowling too short because he generates steepling lift routinely.
Morkel, who took 309 wickets in his career, stands 196cm himself.
He said Jansen's extraordinary success early in spells was due to the nous with which he used his height.
"The reason why he is so successful is that for a tall guy he is really giving the ball the opportunity to do something on a fuller length," Morkel said.
"He knows the batters will at times sit back and stay leg side to use his pace and bounce but he has worked out how to commit them on that fuller length which is why he is so dangerous.
"I didn't have to over-think things in Australia, and he doesn't either, because they are similar conditions to South Africa."
The other aspect that has impressed Morkel is the way Jansen has made an impact from the outset in his career.
"For a youngster coming in you would think it would take him a couple of Test matches to find his feet," he said, "but so far he has been brilliant."
