Bayern took an early lead through Thomas Mueller before Lewandowski struck either side of a Jamal Musiala goal.
Having scored a record 41 Bundesliga goals last season, Lewandowski has already netted five times in three league matches this term.
Lewandowski could have finished with four, having stepped over the ball to allow Mueller to score the early opener.
“Sometimes the first goal is the most important, it was right to leave the ball for Thomas – I knew he was there,” said Lewandowski, who has scored three goals or more in 15 Bundesliga games in his career.
“We had the game under control and everything planned came off.
“I’m always hungry, I feel really good and I am always looking to reach the next level, always ready to improve.”
Mueller said Lewandowski is playing at “another level”.
Lewandowski doubled the lead after Mueller’s opener by heading into the net at the second attempt having first hit the cross bar as Bayern outclassed Hertha.
He has scored in 16 consecutive games for Bayern in all competitions, one more than club late legend Gerd Mueller, who scored in 15 consecutive games in 1969/70.
Hertha’s fortunes did not improve when their goalkeeper Alexander Schwolow landed on Berlin captain Dedryck Boyata after clearing a corner and the pair banged heads.
Bayern’s third came just after the break when Mueller won possession and Musiala, 18, beat two defenders to fire inside the far post.
Musiala made way for Leroy Sane who answered recent whistles from Bayern fans by serving up Lewandowski’s second.
Sane exchanged passes with Mueller, then sliced through the defence on the left and gave Lewandowski a simple tap in for his 300th goal in all competitions for Bayern.
He completed his hat-trick when Joshua Kimmich’s corner was flicked on to the back post by Tanguy Nianzou for Lewandowski to head home.
The rout lifted Bayern into second in the table, level on seven points but behind early leaders Bayer Leverkusen, who swept Augsburg aside 4-1 thanks to two early own goals, on goal difference.
Augsburg made a disastrous start when Brazilian defender Iago, then striker Florian Niederlechner both turned the ball into their own net to generously put Leverkusen 2-0 up after 14 minutes.
Niederlechner made amends when he stabbed home after Leverkusen goalkeeper Lukas Hradecky had rushed off his line.
It was one-way traffic in the second half as Leverkusen dominated with goals by Patrik Schick and Florian Wirtz.
Freiburg are third after a 3-2 victory at Stuttgart, where all the goals came in a frantic first half.
South Korea forward Jeong Woo-yeong, 21, made a dream start with two goals for Freiburg in the opening nine minutes before striker Lucas Hoeler made it 3-0 before half an hour was played.
Stuttgart hit back with rapid-fire goals from striker Hamadi Al-Ghaddioui and defender Konstantinos Mavropanos just before half-time.
Austrian midfielder Patrick Wimmer made a dream Bundesliga debut with Arminia Bielefeld’s equaliser four minutes from time in a 1-1 draw at home to Eintracht Frankfurt.
Wolfsburg can regain top spot if they pick up their third straight league win at home to fellow Champions League side RB Leipzig on Sunday.