Seven-term ruling party legislator and millionaire business executive Chung Mong-joon officially announced his candidacy for Seoul mayor, entering a race that on the same day took an unexpected turn with the announcement of a merger of opposition blocs.

Chung, son of late Hyundai Group founder and current chairman of Hyundai Heavy Industries Co., the world's largest shipbuilder, said he will run for the mayor of the capital city, pledging to put Seoul at the center of national development.

"In order to enter the age of $40,000 per-capita income, the central government and regional governments have to work together hand in hand," Chung said. "National development and people's happiness are possible when Seoul assumes a central role (to achieve the task)."

Local elections will be held on June 4 to elect mayors, governors, education superintendents and heads of regional councils. Because of the nationwide scale, they are viewed as voter's appraisal of the Park Geun-hye administration that just turned one year old on Tuesday.

Just before announcing his candidacy, the main opposition Democratic Party and independent lawmaker Ahn Cheol-soo said they will join forces to create a new party with an ultimate goal of winning the 2017 presidential election. The union has turned what was expected to be a three-way rivalry into a head-on competition between the ruling Saenuri Party and the new opposition camp.

Chung criticized the move, charging that it was the result of the opposition becoming nervous about the election.

"It's regrettable to see Ahn's new politics fall apart in this way," he said.

Chung said he won't be running for president in 2017, dismissing speculation that he would quit midway even if elected as Seoul mayor.

"If elected, I will stick to the given term, and share the joys and tribulations with the people of Seoul," he said. 

Chung is seen as competition against former two-term Saenuri Party legislator Lee Hye-hoon, who already announced her candidacy, and former Prime Minister Kim Hwang-sik, who is said to be on Saenuri's shortlist. (Yonhap)