The ministry said it had comparable data only from 1999, and could not comment on learner numbers since1933.
Dr Graham Stoop, head of student achievement, said: "The drop in numbers in senior secondary can be attributed to the choices students make about which subjects will be most useful to them in the future."
New Zealand did not have a national language policy and learning a language was not compulsory in New Zealand schools at any level.
Dr Stoop said language learning in secondary schools was demand led.
Associate Professor Sharon Harvey, AUT University head of languages, said the decline was "inexorable" and the downward trend "worrying".
"This laissez-faire approach to the delivery of languages in schools could turn to bite us at a time when the market is becoming increasingly globalised," said Professor Harvey.
She said the inability to communicate in another language could hamper New Zealand's international trade abilities, and also affect integration of migrant communities locally.
Professor Harvey said the decline in language learners signalled an "urgent need" for the Government to consider a comprehensive languages policy. "I think New Zealand kids are really underserved by our education system.
"If we looked at any other Asian or European countries, most children are coming out of school with proficiency in at least two and probably three languages."
Professor Harvey said the inclusion of language-learning as a separate area of the New Zealand curriculum in 2007 presented an opportunity for a large-scale review of language-learning pedagogy.
But resignations of key top staff at the ministry who were "pro-language learning" meant that this did not happen.
She did not think the introduction of the 2007 curriculum directly caused the decline, but said the reasons were "complex".
Except for Chinese and Spanish, all other commonly taught languages are on a decline at secondary school level.
But Pacific languages, introduced at some schools mainly to meet community needs, are on the increase.
Education Minister Hekia Parata would not state if she supported a national language policy, but said language learning was a student's choice.
"Ultimately, however, it is up to students, and their parents, to decide which of the many options available at school to pursue," she said.
The minister said she urged all students to consider learning another language as it benefited them and the country.
Chinese trend worries Japanese teachers
Japanese language teachers in New Zealand are worried about losing their jobs, says a senior teacher at a top Auckland boys' school.
Sophie Yoon, who has been teaching Japanese for the past 10 years, four of them as head of the language at Westlake Boys' High School, said some of her colleagues from other schools were worried about the drop in students of Japanese.
The secondary school numbers had declined from 21,121 in 2003 to 11,888 last year, and about 18 per cent fewer secondary schools were offering the subject.
At Westlake Boys', Chinese had become a more popular choice than Japanese since 2012.
A study by the Sasakawa Fellowship Fund in 2013 found that Chinese was replacing Japanese as a language of "extrinsic benefit".
The report said the growth of Chinese as a trade language had affected the numbers learning Japanese.
"Japanese is losing out because parents are feeling that Chinese is more important than Japanese," said Miss Yoon.
Headmaster David Ferguson said Westlake "prioritised" language learning but did not regard one language as more important than another.
