Sehwag (96) and Gambhir (54) added 160 runs for the first wicket before falling in quick succession, leaving Rahul Dravid and Sachin Tendulkar in the middle at the close of the day's play.
The opening pair built on the good work of bowlers Zaheer Khan and Harbhajan Singh, who finished with four wickets each as India took the last six New Zealand wickets for only 92 runs this morning.
Sehwag was a little cautious early on but soon hit the kind of rhythm he is known for. Quick to use his feet, he dispatched off-spinner Kane Williamson for one huge straight six that went ten rows into the stands.
Sehwag had also struck 15 fours when he was bowled by left-arm spinner Daniel Vettori in attempting a swipe to the leg side when in sight of his 23rd test hundred.
If Sehwag was continuing his good form, having struck a blistering 173 in the opening test at Ahmedabad, Gambhir was looking to find his.
The 29-year-old left-hander was scratchy early on and lucky to see Ross Taylor miss a difficult high chance in the slips off Chris Martin when had made just one. But, after a string of low scores that saw him accumulate only 86 in his last nine test innings, Gambhir finally got among the runs to reach his half-century.
He was dismissed the over after Sehwag, however, with the score still on 160, after getting a faint edge to a delivery from seamer Tim Southee that wicketkeeper Gareth Hopkins took down the leg side.
Earlier, Zaheer took the first two wickets to fall before Harbhajan ran through New Zealand's lower order with four dismissals.
Having dismissed centurion Tim McIntosh late on Friday, Zaheer struck again with the second new ball.
The left-armer used the shine to move the ball both ways, removing overnight batsman Gareth Hopkins and first-test centurion Williamson, with both batsmen scoring only four runs. Bowling around the wicket, Zaheer got the ball to move in sharply and trapped them both lbw, to give him figures of 4-69.
Harbhajan removed New Zealand captain Vettori (11) with another lbw dismissal and followed it with three more wickets. Left-hander Jesse Ryder, who scored 70, was taken by V.V.S. Laxman at slip, Southee (10) was stumped by Mahendra Singh Dhoni and last man Chris Martin was caught by Sehwag at leg slip for three.
After going wicketless on the opening day, Harbhajan finished with 4-76.
"It was good to get wickets despite not getting much help from the pitch," Harbhajan said. "Zaheer knows his plans well and got two important wickets for us this morning."
The off-spinner added that Sehwag would not be perturbed at missing out a ton.
"He is a team man and is never bothered about personal milestones," Harbhajan said.
Ryder, who has scored all three of his test centuries against India, was the only New Zealand batsman to play with confidence and was quick to punish the short ball, smashing 10 fours off 120 deliveries.
"We had a bad first session today," Ryder said. "Zaheer bowled a lovely spell and we thought we were 100 runs short in the first innings after a fine opening day."
