China and South Korea have reaffirmed their opposition to North Korean nuclear tests during a visit by Chinese president Xi Jinping which is being seen as a snub to the North.
It is the first time a Chinese leader has visited Seoul before Pyongyang.
South Korean president Park Geun-hye said both countries agreed that the North's denuclearisation should be "realised by all means".
The statement follows a series of missile tests by North Korea.
Mr Xi's visit comes a day after North Korea fired short-range rockets into the sea. Last year, North Korea carried out its third nuclear test and there are reports that it could be planning a fourth.
At a joint press conference with Ms Park, Mr Xi said denuclearisation was a common goal, and must be achieved through dialogue and negotiation.
He called on the six countries involved in the North's nuclear talks to resume negotiations.
South Korea and Beijing differ on how to stop the North's nuclear programme. Seoul would like Beijing to do more to pressure Pyongyang, but Beijing has prioritised stability and encouraged all parties to return to talks without pre-conditions.
Despite their long-standing differences, Mr Xi and Ms Park do appear to be forming a close relationship - announcing new maritime boundary negotiations, a direct currency exchange, and regional economic cooperation, says the BBC's Lucy Williamson.
Mr Xi was accompanied by 250 business executives including Jack Ma, the founder of the Alibaba e-commerce firm, and Robin Li, chairman of search engine Baidu.
The is the fifth summit between the two since both took office. Ms Park visited Beijing last year.
Ahead of the visit, Chinese Foreign Ministry spokesman Qin Gang said that pushing for the denuclearisation of the Korean peninsula remained Chinese policy.
Mr Xi and Ms Park would "fully exchange views" on the nuclear issue and the stalled six-party talks aimed at persuading North Korea to abandon its nuclear ambitions, he said.
But a key issue for China is to maintain stability in North Korea. It fears that regime collapse could propel a flood of refugees across its border and also lead to a unified Korea allied to the US.
So, while its media outlets have in recent months voiced growing concern over Pyongyang's actions, Mr Xi is unlikely to speak out strongly.
A commentary in Chinese state-run news agency Xinhua on Thursday blamed "mutual distrust and hostility" between the US and North Korea for the "chronic" state of the Korean peninsula.