The online video website YouTube has been blocked in China for more than a day, the company said.

YouTube, owned by Google, first noticed a slow down in its traffic from China on Monday March 23 and is now unavailable across the country, a spokesman said.

A Chinese Foreign Ministry spokesman said he did not know about the move, according to Reuters.

"YouTube is currently blocked in China. We don't know the reason for the blockage, but are working as quickly as possible to restore access to our users in China," said YouTube spokesman Scott Rubin.

Both Google and YouTube have previously been blocked in China for brief periods, according to the company. In the past Chinese authorities have blocked specific videos.

A Foreign Ministry spokesman said China's 300 million Internet users and 100 million blogs showed, "China's Internet is open enough, but also needs to be regulated by law in order to prevent the spread of harmful information and for national security".

An internet crackdown that began in January has closed hundreds of Chinese sites, including a popular blog hosting site and several sites popular with Tibetans, according to Reuters.

It has been described by analysts as another step in the Party's battle to stifle dissent in a year of sensitive anniversaries, including the 20th anniversary of the government's bloody suppression of the pro-democracy Tiananmen Square protests in 1989.

YouTube, which has country-specific sites in 23 countries, has in the past been blocked in certain countries, including Turkey and Thailand in disputes over specific videos.