China's President Xi Jinping and South Korean President Park Geun-hye shake hands prior to their summit meeting in Seoul on Thursday. Associated Press

SEOUL—Chinese President Xi Jinping and South Korean President Park Geun-hye on Thursday said they aimed to complete a bilateral free-trade deal by the end of this year and restated their opposition to North Korea's nuclear weapons program.

Mr. Xi arrived in Seoul on Thursday for a two-day visit, the first by a Chinese leader to South Korea ahead of traditional ally North Korea.

At a press briefing after a summit meeting, Ms. Park said that she and Mr. Xi reaffirmed that they "firmly opposed North Korea's nuclear weapons tests."

Mr. Xi read a slightly differently worded joint statement that said both sides "firmly oppose the development of nuclear weapons on the Korean peninsula."

Mr. Xi added that both leaders agreed to make efforts to resume long-stalled six-nation talks-involving China, the U.S., Russia, Japan and the two Koreas—aimed at denuclearizing North Korea.

On the economic front, the two countries agreed to speed up free-trade talks and open a direct won-yuan trading market to deepen a growing business and economic relationship.

As part of the agreement, South Korean institutional investors were granted an 80-billion-yuan quota to invest in the Chinese equities market, the statement.

Seoul previously had no yuan-based quota for its investors to buy Chinese stocks and bonds.

China is South Korea's top trade partner, absorbing about one quarter of South Korean exports. Asia's biggest and fourth largest economies have rapidly expanded their economic ties despite their relatively young diplomatic relationship dating back to 1992.

Mr. Xi's trip to Seoul ahead of Pyongyang was widely seen as a sign of Beijing's displeasure with North Korea under young and hard-line dictator Kim Jong Un, who took power after his father died in late 2011.

Write to Kwanwoo Jun at kwanwoo.jun@wsj.com