A report due to be delivered by Chinese Premier Li Keqiang cuts the country's growth target for this year to around 6.5%, down from 6.5 to 7% last year.
He is due to deliver the report to the country's rubber-stamp parliament, the National People's Congress (NPC), which is gathering in the capital Beijing.
More than 3,000 legislators are meeting in the Great Hall of the People for 10 days, starting on Sunday.
The economy and pollution are among issues expected to be discussed.
The Chinese economy expanded at its slowest pace in 26 years in 2016.
The NPC and its advisory body hold ceremonial meetings every year known as "lianghui" or "two sessions".
The advisory body, the Chinese People's Political Consultative Conference, began its meeting on Friday.
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The growth target was reported by news agencies shortly before the premier was due to speak.
NPC leaders are tolerating slightly slower economic growth this year to give them more room to push through some painful reforms to deal with a rapid build-up in debt, Reuters news agency reports.
State news agency Xinhua said legislators and advisers would, among other issues, discuss globalisation "at a time when certain Western powers are retreating into protectionism and isolation".
The meetings are the first since the election of US President Donald Trump, who has called for higher tariffs on Chinese imports.
Xinhua also reported that national defence and relations with Taiwan, Hong Kong and Macau would be discussed.
Prime Minister Li is also expected to provide more detail on Sunday about the country's defence budget, which is planned to rise by 7%.
This year's "lianghui" comes ahead of a major Chinese Communist Party congress, due to be held later this year.
That congress will confirm party chief and president Xi Jinping's second term in office, as well as announce changes in the party's top leadership.