President Trump chats with Chinese President Xi Jinping during a welcome ceremony at the Great Hall of the People in Beijing. (AP) (Andy Wong/AP)

China is sending a senior diplomat to visit North Korea as an envoy of President Xi Jinping, the Foreign Ministry said Wednesday, reopening a channel of dialogue with the isolated regime.

Song Tao, who heads the Communist Party's external affairs department, will head to Pyongyang on Friday to "inform" the North Korean government about Beijing's recently concluded Communist Party Congress, the state-run Xinhua news agency said. 

The announcement comes a week after President Trump visited China and asked Xi to work hard to rein in North Korea's nuclear weapons program. But the Foreign Ministry said this trip was not connected to Trump's visit.

Beijing routinely undertakes such trips to fellow communist states after key party meetings, and Song has already visited Vietnam and Laos on similar missions.

"The main purpose of the visit is to report on the 19th Party Congress," said ministry spokesman Geng Shuang. He said it was "traditional practice" for China's Communist Party to brief the Korean Workers' Party and parties from other socialist countries after such events. 

Asked if the envoy would meet North Korean leader Kim Jong Un, Geng said he was not aware of the "detailed arrangements" for the trip.

He implied that Song would bring up North Korea's nuclear program.

"He will also exchange views on issues of common interest, such as relations between the two parties and the two countries," he told a news conference.

The visit represents an important opportunity for Beijing to reopen a channel of dialogue with the isolated regime, experts said, as relations between the countries have deteriorated significantly in recent years.

China has an official special envoy to North Korea, Kong Xuanyou, but he is not believed to have visited Pyongyang since taking the job in August. His predecessor, Wu Dawei, last visited North Korea in February 2016. Song's visit will be the first by a ministerial-level official since then-Politburo Standing Committee member Liu Yunshan went to Pyongyang and met Kim in October 2015.

Xi is believed to be frustrated with North Korea's aggressive development and testing of its nuclear weapons and missiles, and he has imposed a relatively strict set of sanctions under U.S. pressure and in line with U.N. Security Council resolutions. 

But China still dominates trade with North Korea and is unwilling to cut off the regime's economic lifeline, symbolized by a pipeline that supplies the crude oil keeping the country's military and industry afloat. 

It does not want to see a fellow communist regime and long-standing ally toppled, but it equally does not want the current regime to turn hostile and threaten China with its nuclear weapons and missiles.

"They still want to balance and they want to maintain some channels," said Paul Haenle, director of the Carnegie-Tsinghua Center in Beijing. "Relations have really deteriorated, and the Chinese recognize that. They don't want relations to fall apart."

Haenle said the visit might include some "sweet talk" for Pyongyang about working together. But he predicted that the Chinese would also make their displeasure known. 

Wang Sheng, a North Korea expert at Jilin University in Changchun, said communications between Beijing and Pyongyang improved after the Party Congress when Kim sent Xi a congratulatory message and Xi sent his thanks in return. He said China could use the trip to "persuade the North to return to the negotiation table as soon as possible."

While in Beijing, Trump said China can fix the North Korea problem "quickly and easily," and he urged Xi to "work on it very hard."

After leaving China, he suggested that more action by Beijing was coming. "President Xi of China has stated that he is upping the sanctions against #NoKo. Said he wants them to denuclearize. Progress is being made," Trump tweeted Saturday.

Luna Lin contributed to this report.