China has been a strong performer among emerging economies, even if its growth has been slowing. But that's set to end, according to research firm Capital Economics.

Growth in China could plummet to 2 percent over the next decade — from the expected 6.0 to 6.5 percent target this year, predicted Capital's Chief Asia Economist Mark Williams.

"China's time as an emerging markets outperformer is ending," said Williams, at the Capital Economics annual conference in Singapore on Tuesday. He added that the estimated 2 percent growth is a "long way" from the 5 to 6 percent expected by the International Monetary Fund for the next decade.

Speakers at the conference pointed to a number of risks, as well as changing demographics in the world's second largest economy. That includes its debt problem, declining work force, and increasingly weaker drivers of productivity, they said.

Those predictions come as Chinese Premier Li Keqiang said at the annual National People's Congress on Tuesday that the official economic growth target this year will be 6.0 to 6.5 percent, slowing from last year.

Li also warned that there will be greater risks ahead for the Asian economy, saying: "We must be fully prepared for a tough struggle."