As you may already know, the end of the world starts today - but that's no reason to put off mowing the lawn.

American preacher Harold Camping has predicted that Judgment Day will start on May 21 with a series of earthquakes in New Zealand which will spread around the world, killing everyone but true believers.

His Family Radio organisation has spread its message in many countries, including New Zealand. Followers have written warnings for the Herald's letters page and paid for a billboard near the popular St Lukes shopping mall in Auckland.

Critics have pointed out that the veteran religious broadcaster's prediction relies on a dubious numerological interpretation of the Bible, which has been ridiculed by scientists and mainstream churches. So how will he react tomorrow when the world carries on as normal?

NZ Skeptics chairwoman Vicki Hyde says history shows Camping will have no shortage of excuses.

She says William Miller, the founding father of modern doomsday predictions, forecast the end of the world three times in 1843 and (twice) in 1844.

The third false prediction became known as the Great Disappointment. But despite Miller's poor track record, many of his followers continued to have faith in him. Several churches, including the Seventh Day Adventists, can trace their origins to his beliefs.

Hyde notes that Camping, 89, has predicted the end of the world before, in 1994. When nothing happened he said he had done his calculations wrong and plumped for May 21, 2011.

"I'm wondering if he didn't expect to be around to live through another Great Disappointment."

It takes a lot to shake the convictions of doomsday followers, as psychologist Leon Festinger and his colleagues found in the 1950s when they infiltrated the Seekers, a small Chicago-area cult whose members thought they were communicating with aliens.

Cult leader Dorothy Martin had predicted that the world would end on December 21, 1954, and the group would be rescued and taken away in a flying saucer.

Festinger wanted to see what would happen when the group's entire belief system was proved wrong. He found their first reaction was shock, quickly followed by the rationalisation that their devotion had saved the world from the prophecy.

"Your philosophers will call that ad hoc reasoning," says Hyde. "Most of us will say that's pretty weasel wordy."

She worries that while many people treat the prediction as amusing, members of religious and new age cults have been known to commit suicide, either in preparation for the end of the world or disappointment when it fails to happen.

She was talking this week to an American radio station, which believed there was a risk among Camping's followers, who saw the destruction of all life on earth as a gateway to a better life with God.

"Most of them do want the rapture. We just hope they don't try to help it along, one way or another."

She believes doomsday predictions will continue after this weekend, as many forecasters have picked 2012 (already popularised by a film of the same name), supposedly based on interpretations of the ancient Mayan calendar.

Cultwatch director Mark Vrankovich says he's not aware of any New Zealanders preparing for the end of the world in response to Camping's prophecy. He believes the risk of suicide is low but worries that some people might break off relationships or sell their houses.

"You invest a lot of your emotional energy or put money into it. So no matter what the evidence you want to keep on believing. The alternative is that you've wasted your time and money, you've wasted friendships and burned bridges - people don't want to face up to that."

Cultwatch is a Christian organisation, which warns people on its website not to base their faith on a false premise.

On the site Vrankovich says the prediction is partly based on an obscure Biblical reference to Jesus' disciples fishing 200 cubits (1 cubit = 45.72cm) out from the shore on the Sea of Galilee (John 21: 1-14), which Camping has decided means there will be a 2000-year gap between the first and second coming of Christ.

"Not only has Harold Camping inserted his own meaning into a minor detail in the Bible, he has changed the number from 200 to 2000 and the units from cubits to years. With 'reasoning' like this it is amazing that anyone has taken Harold Camping seriously."

Top five failed Judgment Day predictions

1 The Prophet Hen of Leeds, 1806

A hen in the English city of Leeds supposedly began laying eggs on which the phrase "Christ is coming" was written. Many people became convinced that doomsday was at hand - until a curious local watched the hen laying one of the prophetic eggs and discovered someone had hatched a hoax.

2 The Millerites, April 23, 1843

New England farmer William Miller concluded the world would end some time between March 21, 1843 and March 21, 1844. Thousands of his followers, known as Millerites, sold or gave away their possessions, assuming they would not be needed. After the third prediction failed on October 22, 1844, many Millerites drifted away but the movement inspired several later religions, including Seventh Day Adventists and Jehovah's Witnesses.

3 The Seekers, 1954

A small group led by Chicago housewife Dorothy Martin believed the world would end in a great flood before dawn on December 21, 1954, but her group would be rescued by aliens from the planet Clarion in a flying saucer at midnight. The group carefully removed all metallic items from their clothing - such as zips and bra clasps - in preparation for boarding but the flying saucer failed to appear.

4 Pat Robertson, 1982

In May 1980, televangelist and Christian Coalition founder Pat Robertson startled his global audiencewhen he announced on his "700 Club" TV show: "I guarantee you by the end of 1982 there is going to be a judgment on the world." In 1988, unfazed by his failed prediction, he ran for the Republican Party presidential nomination.

5 Heaven's Gate, 1997

When comet Hale-Bopp appeared, rumours surfaced it was being followed by an alien spacecraft. These claims inspired a San Diego UFO cult named Heaven's Gate to conclude that the world would end soon. Thirty-nine of the cult members committed suicide on March 26 that year.