(Image Credit: ChinaFotoPress/Getty Images)

ABC News' Gloria Riviera reports:

BEIJING - What officials say were false terror threats against three domestic carriers led to significant delays and cancellations at many of China's main airports today. Authorities are still investigating calls made to China Eastern Airlines, Juneyao Airlines and Shenzhen Airlines.

They say no one and no plane was ever in real danger. Chinese airlines have been targeted in the past. A man convicted of a bomb hoax last year, for instance, received a four-year prison sentence.

Passengers in Shanghai's Pudong International airport waited for hours without any explanation. But that is not unusual in China, where extreme air rage is increasingly common.

See this photo of a gate agent in the fetal position after a fight with angry passengers.

In China, air travel is like car ownership was in the 1990s. Air travel is cheaper and millions are choosing to fly instead of taking the train.

But the service industry has a long way to go here, and passengers routinely go, well, a little crazy. About 20 people stormed the runway last year in front of an oncoming plane.

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Staff are routinely assaulted (it seems every week there is a new video of airport brawls) and a state official was caught on camera recently going ballistic in front of his own family. He was later reprimanded with a heavy fine.

Manufacturers estimate that a new plane will take to the skies every other day for the next decade to service millions of domestic fliers. That has caused concern about already clogged routes and limited air space.