End of the world is very nigh indeed...

If the world's going to end, you might as well go down smiling.

So says Chris McNaboe, a postgraduate student from Monterey in northern California, who has invited friends to spend this evening at his home, eating, drinking, and making merry in celebration of an apocalypse that is scheduled to commence at 6pm.

Mr McNaboe this week paid a small fee to an internet site that allowed him to be ordained as a minister in the Universal Life online church. At tonight's party, he will therefore be baptising guests in his paddling pool in a last-ditch effort to save their souls. "It was kind of God to give us this excuse for a party," he says.

Not everyone gets the joke, though. A couple of hours north Monterey, in a large house not far from Oakland airport, a famous evangelical preacher called Harold Camping will be spending this evening surrounded by close family members, praying, reading from the Bible, and keeping an eye fixed on CNN.

When the clock strikes 6pm, Mr Camping believes that a large earthquake will indicate the Second Coming of the Lord. Roughly 2 per cent of the world's population will be immediately "raptured" to Heaven, he predicts. The rest of us will endure a few months of fire and brimstone here on Earth, before being sent to the fiery pits of Hell.

Mr Camping, who is 89 and uses hearing aids in both ears, is not the first self-proclaimed prophet to call the apocalypse. Neither, given his track record, is he necessarily the most reliable. But thanks to his skill at persuading followers to part with large amounts of their time and money, he happens to be one of the hardest to ignore.

Each weekday, Mr Camping, a former civil engineer, preaches to hundreds of thousands of followers from the studios of Family Radio, a broadcaster funded entirely by the donations of listeners which has its headquarters between a burger restaurant and a car repair shop.

Such is the generosity of listeners that his organisation, founded in the 1980s, has over the years acquired $120m (£74m). Its programming is carried on the airwaves of 66 radio stations in the United States, and roughly 80 more around the world, in 48 different languages.

That gives Mr Camping quite a pulpit. In recent months, Family Radio has paid for roughly 2,500 billboards to carry slogans such as "Blow the Trumpet! Warn the People!" Advertisements in major newspapers have for most of the past week instructed readers to: "Cry Mightily unto the Lord for Mercy!"

A fleet of 30 buses has meanwhile been touring the country, warning of the impending apocalypse. Two of them are currently parked in Times Square, spreading the word to the sinners of New York. Their message is capturing the public imagination, and being lapped up by news networks.

"In the Bible, the Lord says to 'occupy until I come'," Mr Camping tells The Independent. "So my business is to carry on saving souls as long as I can. The end is now getting real close, and we'll find out whether we're going to be eternally dead, or eternally alive. That's pretty awesome, when you start to think about it!"

Mr Camping was born a Baptist, but split from organised religion in the 1980s. A Biblical literalist, he now advocates home worship. Many of his views – he is against abortion, thinks evolution is a hoax, and says sex outside of marriages is an "abomination" – are relatively common among mainstream Republican voters.

The conviction that the world will end at 6pm today comes from a mathematical system he claims to have devised for unearthing prophesies hidden in the Bible. By his logic, 21 May 2011 is exactly 722,500 days from 1 April AD33, which he believes was the day of Christ's Crucifixion. The figure of 722,500 is important because you get it by multiplying three holy numbers (five, 10 and 17) together twice.

"It's all here, in black and white," he says, waving a well-thumbed copy of the Old Testament.

Mr Camping has encouraged followers to quit their jobs and tour the country saving souls. The roughly 225 employees of Family Radio have been kept on the payroll, but told to stop making new programmes and head on to the streets spreading the word. For obvious reasons, the organisation hasn't been sending out post, or paying bills, for the past couple of weeks.

Asked for further evidence that Judgment Day is approaching, Mr Camping cites recent natural disasters, including the earthquakes in Japan, New Zealand, and Haiti. "But believe me," he adds, "the earthquake on 21 May will make them look like a Sunday-school picnic."

God's decision to call time on the world is hastened by declining social values, Mr Camping argues. The Gay Pride movement was "sent by the Almighty" as a sign of the end. So was "all the stealing, lying, wickedness and sexual perversion" that has accompanied the recent internet revolution.

"When I was young, you had to go out to a theatre some place if you wanted to look at raunchy movies," he says. "Today, you can watch pornography on a computer in your bedroom. Nobody sees you. And these films... they contain the most horrible perversity you can ever, ever imagine."

Mr Camping predicts that the world will end at 6pm local time in whatever part of the globe you happen to be. He therefore plans to wake up in time to witness Armageddon strike New Zealand. He will then spend his day watching CNN coverage of it sweeping across the time-zones.

Cynics point out that this isn't the first time Mr Camping has called the Second Coming. In 1994, hundreds of his followers gathered in Alameda to await Christ's return, only to have to sheepishly go home when the world failed to end.

This time he claims 17 years of further study have given him "outstanding proofs" that the end really is nigh. "At that time there was a lot of the Bible I had not really researched very carefully," he says. "But now, we've had the chance to do just an enormous amount of additional study."

Apocalypse Not

*1844: Thousands of Americans gave away all of their possessions after a preacher in the Millerite movement claimed to have determined the date of the apocalypse as 22 October, 1844. In hindsight, the day became known as 'The Great Disappointment'.

*1954: A follower of L. Ron Hubbard, the founder of Scientology, claimed aliens told her the world would end on 21 December, 1954. Believers gathered at her house to wait for the said aliens to land, and even removed metal components from their clothes in fear of being burned in the radiating heat of the flying saucers. When nothing happened, she told the crowd that God – impressed by their actions – had decided to spare the planet. Her husband (a non-believer) reportedly slept through the entire episode.

*1982: The US televangelist Pat Robertson told viewers of his Christian TV show that "a judgment on the world" would pass by the end of 1982. He continues to host the same show.

*1997: Believing an alien spacecraft was following the Hale-Bopp comet, San Diego-based cult Heaven's Gate declared the end of the world was nigh. Its leader, Marshall Applewhite, persuaded 39 cult members to enter into a pre-emptive suicide pact. For them, the world did end when they took their own lives on 26 March 1997.

Enjoli Liston