Half centuries by Kusal Mendis and Dimuth Karunaratne have helped Sri Lanka reach 6-305, taking the upper hand on the first day of the first Test against New Zealand in Christchurch.

Mendis made 87 and captain Karunaratne 50 and they shared a critical partnership.

At stumps - after only 75 overs in the day - Dhananjaya De Silva was 39 not out and Kasun Rajitha was unbeaten on 16, his highest Test score.

New Zealand captain Tim Southee said the pitch at Hagley Oval had a "green tinge" and he was happy to send Sri Lanka in and take the new ball as part of a Black Caps attack bolstered by a fourth seamer.

Sri Lanka lost an early wicket and scored only 27 runs in a watchful first hour.

But Mendis went on the attack in the second hour and reached his 16th half century from 40 balls as the visitors reached 1-120 at lunch.

A 137-run partnership between Mendis and Karunaratne lifted Sri Lanka to 2-151 before both batsmen were out at that score as Southee and his new ball partner Matt Henry struck back.

Angelo Mathews and Dinesh Chandimal, slowly at first but with growing confidence, built a partnership worth 58 runs by tea when Sri Lanka were 3-210.

Rain briefly delayed the return of players from the tea break but passed quickly and the partnership was 82 when Chandimal was caught by Tom Latham off Southee for 39.

The wicket was Southee's 362nd in Tests, taking him past former spinner Daniel Vettori into second place on New Zealand's all-time list of Test wicket-takers behind Richard Hadlee (431). Southee also passed Vettori's mark of 705 to become New Zealand's leading wicket-taker across all three formats.

Mathews also reached an important milestone when, at 47, he passed 7000 runs in Tests, achieved at an average of 45.

He was out at that score, caught by Latham at second slip off Henry and Niroshan Dickwell fell soon after for seven, lbw to spinner Michael Bracewell.

The use of Bracewell was a necessity caused by the ineffectiveness of New Zealand's fourth and fifth seamers Neil Wagner and Daryl Mitchell.

Wagner was the hero of New Zealand's one-run win over England in the second Test in Wellington two weeks ago. But he took a pounding on Thursday, conceding 68 runs from 10 overs.