Munich:Reigning Formula One champion Lewis Hamilton is "unbeatable" when at his best, according to his Mercedes team's executive director Toto Wolff. The reigning world champion has surged into the lead of the 2016 title race by matching the best winning run of his career with six victories from the last seven races. Hamilton's win in Sunday's German Grand Prix, the 49th of his career, meant he has taken a 19-point advantage over Mercedes team-mate Nico Rosberg, having fallen 43 points adrift after the season's opening four races. "On a good day I think that he's unbeatable. But then it's still a mechanical sport and he's a human and you can have bad days and worse days and this is why he is not winning every single race," Wolff was quoted as saying by Sky Sports on Sunday. Amid a series of poor starts, collisions and other technical problems, Hamilton had to wait six races before registering his first win of the ongoing season, at Monaco in May. Four of Rosberg's five wins came at the start of 2016. Wolff added, "I really admire the way it's going, the ping-pong between those two, and the way they keep coming back". When F1 returns from its four-week recess at the Belgian Grand Prix on August 28, the challenge for Rosberg will be to end the momentum which has seen Hamilton put himself on course for a third straight championship win. Although acknowledging the difficulty in beating an on-form Hamilton, Wolff replied with "a big yes" when asked if Rosberg can fight back in the title race. "We have seen him start the season extremely well and he had an end of the season in 2015 that was very good. There are still nine races to go - it's more than 200 points to collect,” Wolff said.