The Tottenham striker took his tally to 31 with a hat-trick in the 7-0 win over Montenegro on Thursday.
Kane is now fourth on the all-time scorers list, and Southgate thinks he can surpass Wayne Rooney's total of 53.
"It's an amazing feat [by Kane] when you're talking about the names [Shearer, Finney and Lofthouse]," Southgate told Sky Sports. "It's lovely on a night like tonight that we can talk about those players.
"He is ruthless, he's got the ability to do it, he's got time. If everything falls into place for him, I'm sure he can do that."