The requirements included being readable on smaller phone screens, not using software that was not compatible with mobiles and having links spaced out to make searching on mobiles easier for users.
Griffin said that although websites would not disappear from Google when searching on mobile, for some companies, not being on the first page of Google's search could be devastating.
Auckland marketing consultant Fleur Revell from Impact PR said she had looked over websites of the NZX's top 50 companies earlier this month and found half failed Google's online mobile readiness tool.
"Dynamic businesses that can adapt rapidly to Google's 500 algorithm changes each year will reap the rewards, while others will be relegated to virtual obscurity as their rankings slip off the coveted first page of Google."
Revell said a quarter of the retail brands surveyed also failed to meet the requirements.
She said the biggest risk was for businesses that relied heavily on marketing directly to consumers and on bricks-and-mortar stores that used mobile searches to drive foot traffic through their doors.
"Retail is a particularly competitive industry and in the case of a shopping mall or district, mobile search-driven foot traffic has become a key driver of sales," Revell said.
"Those sites which are mobile-friendly can expect a significant boost in mobile search engine rankings, site traffic and potentially sales."
Griffin said updates could vary in difficulty depending on the complexity of the website.
He expected other search engines would follow suit, but Google's deadline of today was "the first red flag" for businesses to ensure their sites were mobile-friendly.