Across the U.S. and in places around the world, signs and newspaper ads have been warning that judgment day is coming on May 21, 2011.

Harold Camping, the head of a Christian broadcast group called Family Radio, has been predicting for years that the event would take place on that day, although in 1994, he incorrectly predicted it.

Japan's earthquake in March will look like a Sunday school picnic in comparison, he told CBS Atlanta on Wednesday.

Robert Jeffress, a pastor at the 13,000 member First Baptist Church, in Dallas, Texas, wrote in a CNN column that such predictions give non-Christians one more reason to discount the Bible.

In addition, he says Camping's false prediction discourages people from taking the steps necessary when the real event occurs.

That is why God refuses to show us his calendar and instead instructs us to focus on our assignment, he wrote.

The rapture, which Camping says will take place on that day, will take believers from earth into heaven. The non-believers will remain on earth until October 21, 2011, when the world will end, Camping says. During the five month period, the earth will suffer great natural disasters, he says.

Camping adds that the righteous - which are only 3 percent of all people - will be swept up.

Our job is to do everything possible to try to warn the world of this terrible terrible tragedy that is ready to unfold, he said.

Camping says people need to pray and be saved.

People should be praying and begging God, he said.

Camping previously wrote a book in 1994 which predicted the end of the world that year.

I hurriedly wrote a book, 1994, but I put a question mark after it, he said.

Albert Mohler, President of the Southern Baptist Seminary, says two Bible verses forbid Christians to claim the knowledge of such dates and times.

Christ specifically admonished his disciples not to claim such knowledge, Mohler wrote in his blog.

In Acts 1:7, Jesus said, 'It is not for you to know times or seasons that the Father has fixed by his own authority.' He said in Matthew 24:36, Christ taught similarly: 'But concerning that day and hour no one knows, not even the angels of heaven, nor the Son, but the Father only.'

Mohler cites another passage in Hebrews 9:28, which states that Christ will come for a second time to save those who are eagerly awaiting him.

Mohler says it is the task of Christians to share the Gospel and live faithful Christians lives.

The church is not to be arrogantly setting dates, but instead to be eagerly waiting for him, he wrote.