The 33-year-old has 8124 career runs and sits 32nd on the all-time list (next is England duo Kevin Pietersen 8181 and David Gower 8231),
Williamson could also become the second New Zealander since Andrew Jones to score three successive hundreds. Jones scored 186, 122 and 100* against Sri Lanka in 1991. Everton Weekes is the only man to score five straight tons.
Other potential test milestones this summer
Test matches
The first test in Bangladesh is the 95th test appearance for both Williamson and Tim Southee. They would need to play all six tests across the summer to reach 100 for the second test against Australia in Christchurch. Seventy-five players in test history have made 100 appearances, including four Kiwis - Daniel Vettori (112), Ross Taylor (112), Stephen Fleming (11) and Brendon McCullum (101).
Tom Latham is playing in his 75th consecutive test, the New Zealand record is 101 by McCullum.
Batting
Latham (5150 runs) is 184 runs shy of John Wright (sixth all-time for New Zealand).
Nicholls needs 52 runs to become the 16th New Zealander to reach 3000 runs.
Tim Southee needs 24 runs to reach 2000 test runs. He would be just the fourth man in test cricket to do so without scoring a century.
Southee is one six behind Vivian Richards (84) to move into ninth on the all-time list for sixes, and four behind Chris Cairns (87).
Bowling
Southee has 370 test wickets - three shy of Waqar Younis (21st overall) and six behind Malcolm Marshall (20th).
In the first innings in Sylhet, Ajaz Patel became the 40th New Zealander to take 50 test wickets.
Listen to ball-by-ball commentary of every home Black Caps match this summer live and free on iHeart Radio with The Alternative Commentary Collective.