Kazakhstan's long-serving President Nursultan Nazarbayev apologized on Monday for winning re-election with 97.7 percent of the vote, saying it would have "looked undemocratic" for him to intervene to make his victory more modest.

Sunday's election gives another five-year term to the 74-year-old former steelworker, who has ruled the oil-producing nation since rising to the post of its Soviet-era Communist Party boss in 1989. Central Election Commission data showed turnout was 95.22 percent.

Television showed a triumphant Nazarbayev walking on a red carpet, smiling and shaking hands and greeting thousands of jubilant supporters at what officials called "The Victors' Forum" held in a spacious stadium in the capital Astana.

"Kazakhstan has shown its political culture to the entire world," he told his supporters.

At a later news conference, he said of the poll results, "I apologize that for super-democratic states such figures are unacceptable. But I could do nothing. If I had interfered, I would have looked undemocratic, right?"

Russian President Vladimir Putin and Chinese President Xi Jinping promptly congratulated Nazarbayev on his re-election.

China is willing to maintain ties after Nazarbayev's victory, said Chinese foreign ministry spokesperson Hong Lei at a news conference Monday.

"The Chinese side respects the choice made by the Kazakh people, and supports Kazakhstan in pursuing a development path that suits its national conditions. It is believed that Kazakhstan will maintain political stability and economic development, and play a bigger role in international affairs," Hong said. "Being comprehensive strategic partners, the two countries have established good relations that have developed quickly and healthily," Hong said. China stands ready to work with the Kazakh side to bring Sino-Kazakh relations to a new level, Hong added.

Nazarbayev has promoted market reforms and attracted $200 billion in foreign direct investment, turning his nation of 17 million into the second-largest economy in the former Soviet Union and No.2 post-Soviet oil producer after Russia.

Nazarbayev has promoted "a multi-vector policy," building good ties with neighboring Russia and China as well as the US and the European Union.

Kazakhstan's economy has been hurt in the past year by the decline in global energy prices and by economic difficulty in  Russia, hit by Western sanctions over Ukraine.

The election was called more than a year before Nazarbayev's term was due to end, averting the risk that another year of economic pain could develop into a more serious challenge to his leadership.

Kazakh economic growth is forecast to slow to 1.5 percent this year from a 4.3 percent rise in 2014. Gross domestic product may actually shrink if oil prices drop to below $50 per barrel, Kazakh officials said.

Nazarbayev moved to allay speculation about a further depreciation of the national tenge currency. Kazakhstan devalued the tenge by 19 percent in one move in February 2014, but since then the currency has strengthened against Russia's sanctions-hit ruble, fueling speculation of a further depreciation after the early election.