China temporarily banned the letter N from being published online after people started using it to criticize a plan which paves the way for Xi Jinping to rule the country indefinitely, Business Insider says.

The Chinese Communist Party proposed to abolish the two-term term limit for the president and vice-president, sparking an online backlash which it has been trying to control.

Critics flooded Weibo and WeChat — China's version of Twitter and WhatsApp — to protest the plan, but were swiftly met by the country's censors.

Various Chinese characters for terms like "emigrate," "lifelong," and "I disagree" were banned, alongside ... the letter N.

The screenshot underneath shows a user on Sunday attempting to type "N" into Weibo, and receiving an error message that the "content is illegal."

The other words that appeared to be banned in the screenshot are: "Xi JinP," "emigrate," and "indefinite control."

As of Tuesday morning local time (CST), China had lifted its ban on N again.

The letter is used in China to represent unknown numerical values, like the letter X in algebra.