Mentions of North Korea's first lady, Ri Sol-ju, have been removed from Chinese social media after she travelled to Beijing with her husband for a surprise visit.

Kim Jong-un met China's president, Xi Jinping, in his first trip outside the isolated state since he came to power in 2011.

Ms Ri and Peng Liyuan, China's first lady, were photographed a number of times during the two-day meeting.

Ri Sol-ju with her husband, Kim Jong-un, as they walk with China's president, Xi Jinping, and his wife, Peng Liyuan (EPA/KCNA)

Their outfits and looks attracted comments on popular social media site Sina Weibo.

One user said Ms Ri had "a powerful presence" in addition to being prettier and better dressed than Ms Peng.

Others compared Ms Ri's looks to those of popular South Korean and Chinese actresses.

Another Weibo user wrote: "Ri Sol-ju is indeed beautiful and amiable. I can tell she would be good at 'first-lady diplomacy', better than Kim's sister."

When the train carrying the North Korean leader in his wife arrived in Beijing, it was initially rumoured to have brought his sister, Kim Yo-jong.

Ms Kim represented the North at the Winter Olympics in South Korea.

Mentions of Ms Ri's name were later blocked on Weibo and comments on online news reports were removed.

They remained blocked on Thursday.

Kim Jong-un and his wife, Ri Sol-ju, were treated to a lavish welcome by China's president, Xi Jinping during a secretive trip to Beijing (AFP PHOTO/KCNA VIA KNS)

William Tang Tat-chi, a fashion designer in Hong Kong, described Ms Ri's fashion sense as "subtle" but not conservative, according to the South China Morning Post.

Mr Tang said although her looks were "outdated," they were nevertheless impressive considering she came from a totalitarian country.

Ms Ri was filmed in at least three different outfits during her stay.

From left to right: North Korea's leader, Kim Jong-un, and his wife Ri Sol-ju, left, talk with Chinese counterpart Xi Jinping, and his wife Peng Liyuan, at the Great Hall of the People in Beijing (Korean Central News Agency/Korea News Service via AP)

She first wore a camel-coloured jacket with matching skirt while Ms Peng wore a coat with black ink splotches.

As they visited the Chinese Academy of Natural Sciences, Ms Ri wore a white jacket with a green dress.

She later wore an ivory suit with a flared waist and sleeves to a lunch at the Daioyutai State Guesthouse, where they stayed.

Ms Ri is believed to have married the supreme leader of North Korea in 2009.

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During the state visit, Mr Kim pledged to denuclearise the Korean peninsula.

The comment was reportedly widely in Chinese state media, although North Korea's official media made little mention of it.

A senior Chinese official who visited Seoul on Tuesday to brief South Korea on Mr Kim's visit to Beijing said it should help ease tensions and lead to denuclearisation of the peninsula.

"We believe his visit will help... ensure peace and security of the Korean peninsula and resolve problems regarding the peninsula through political negotiations and discussions," Yang Jiechi said during a meeting with the head of South Korea's National Security Office, Chung Eui-yong.