Clarkson, the 27-year-old middle-order batter and medium-pace bowler, has played three ODIs and T20Is while 26-year-old Smith has yet to make his international debut.

"Nathan's been on our radar for a while having been a significant performer in domestic cricket for some time," New Zealand head coach Gary Stead. "He's been particularly impressive in red-ball cricket and we think he has the skills to be successful in international cricket when he gets a chance."

Clarkson, meanwhile, featured in series against Bangladesh, Australia and Pakistan last season.

"Josh has been involved in both white ball squads over the past twelve months which shows the strides he's made in his game," Stead said. "He's a hard-hitting player with plenty of skills and has shown in his chances so far that he can offer a lot with bat and ball on the international stage. Josh will provide depth and adds value given the volume of white ball cricket on the horizon."

The vacancies on the contract list arose when Conway and Allen opted out in order to take up T20 league deals during January. Conway, who will play in the SA20 for Joburg Super Kings, was offered a casual playing contract, the same model given Kane Williamson. Allen, who signed a two-year deal with Perth Scorchers in the BBL, wasn't provided the same option but will remain eligible or selection on a case-by-case basis.

Updated New Zealand Men's central contracts

Tom Blundell, Michael Bracewell, Mark Chapman, Josh Clarkson, Jacob Duffy, Matt Henry, Kyle Jamieson, Tom Latham, Daryl Mitchell, Henry Nicholls, Will O'Rourke, Ajaz Patel, Glenn Phillips, Rachin Ravindra, Mitchell Santner, Ben Sears, Nathan Smith, Ish Sodhi, Tim Southee, Will Young