Jarvis, 20, sunk six birdies and a single bogey on Friday on the par-four 17th as he seeks of a first victory on the European circuit. He will enter the weekend on 10 under-par for the tournament.
That is a stroke ahead of England's Marco Penge, who carded the joint low round of the day with a superb 66, sinking an eagle on the par-five 15th.
A quartet of players are a further stoke back, including former Masters champion Charl Schwartzel (68) and South African amateur Christo Lamprecht (69), who won the 2019 Junior Golf World Cup in Japan with Jarvis.
New Zealand's Sam Jones made the cut with a shot to spare despite following up his superb first round 67 with a 75.
"I've hit a lot of good shots, but I've hit some really bad ones and I've kind of got away with that a little bit," Lamprecht said.
"I guess I've been a little bit lucky on some holes for sure but I've used that luck, I've played really smart golf."
Lamprecht, 22, took the Low Amateur honours at last year's British Open and is determined to stay in contention through the weekend.
"Last week at the South African Open I didn't play too great and I didn't have a chance to play the weekend, so I'm looking forward to playing this weekend and putting a good showing in," he said.
Defending champion Ockie Strydom failed to make the cut after a second round 78 left him five over-par for the tournament.
