He hit 23 maximums in his 281 from 167 balls for Auckland against Central Districts in the Plunket Shield - New Zealand's first-class competition.
The previous record of 16 was held by four players - Andrew Symonds, Graham Napier, Jesse Ryder and Mukhtar Ali.
Munro, 28, not in New Zealand's World Cup squad, will play for Worcestershire again in this year's T20 Blast.
The left-hander made 13 appearances for the county in last year's competition, scoring 332 runs at an average of 27, with a top score of 65.
He played one Test and seven one-day internationals for New Zealand in 2013, with a highest score of 85 in an ODI against Bangladesh.
Munro has also made 14 T20 international appearances, averaging 21.55 with a highest score of 73 not out, but has not featured since the ICC World Twenty20 last year.
New Zealand batsman Colin Munro has smashed the record for the most sixes in a first-class innings.