A New Zealand mathematician who predicted the deadly Christchurch quake has terrified Kiwis with news another will strike the city in two weeks.

Popular long-range weather forecaster Ken Ring is warning that a second jolt will hit the already-devastated South Island city on March 20.

Mr Ring, who lives in Auckland, uses the moon, sun and tidal activity for the basis of his theories, which have been dismissed by scientists.

His warning is clear.

"If I lived in Christchurch, I'd get out for a few days over that time, go camping, visit friends, just get out and keep safe," he said.

"And if you don't live there, stay away."

His frightening words have panicked New Zealanders, with hundreds using Twitter and Facebook to brand his theories as "crackpot", "wacky" and scientifically baseless.

Despite this, his following is substantial, with more than 5000 New Zealanders - including farmers, gardeners and even disaster specialists - signed up to receive his weather predictions.

On Valentine's Day, he issued a tweet stating that conditions were "potent" for a quake in Christchurch between February 15 and 25.

A 6.3-magnitude earthquake struck on February 22, killing as many as 240 people.

Eerily, he warned people to watch for "special signs", such as silent birds or scared pets, and said "stay away from old cracked buildings".

His words have sparked ferocious debate. Some, like prominent current affairs host John Campbell, believe his frightening words prey on vulnerable people struggling to recover in the wake of the disaster.

But when Campbell threw tough questions at Mr Ring on national television on Monday, giving him no chance to answer, hundreds of Kiwis came to the defence of the so-called Moon Man.

Campbell was forced to apologise, admitting he didn't believe Mr Ring's theories.

"But many people I've spoken to do - and Mr Ring's predictions terrify them," the broadcaster said, before begging him to "stop scaring people".

And scaring them he is. Elderly Australian Gloria Cotton survived the quake and said that predictions of another were "ghastly".

"Tell them to stop, please just stop," the 84-year-old said from her damaged Christchurch home.

"Life is so hard anyway. We can't cope with hearing about another one."

Mr Ring for his part said he believed most people would rather be safe than sorry.

"If the information was there wouldn't you rather have access to it?

"How terrible would it be if I knew all the seismic signs were there and I didn't say anything? I couldn't live with myself.

"If you'd rather not know, then please don't read it."

The scientists, however, remain unconvinced.

Dr Mark Quigley, senior lecturer in active tectonics and geomorphology at the University of Canterbury in Christchurch, said Mr Ring's assertions were "ludicrous".

"Vague quotes about dates of 'increased' activity plus or minus several days, without magnitudes, locations, and exact times do not constitute prediction," Dr Quigley said.

"This is opportunistic and meaningless self promotion during a time of national crisis.

"I won't be going anywhere in late March."