China's Parliament will intensify oversight of the government's work this year in areas such as pollution control, while speeding up work to compile the country's civil code by 2020, its top legislator has said.

Addressing almost 3,000 delegates in the Great Hall of the People following a historic vote that abolished term limits for the presidency, National People's Congress (NPC) chairman Zhang Dejiang hailed the legislative body for drafting the amendments to the Constitution.

Mr Zhang noted that the NPC began work on the draft changes in late January, on the instructions of the Central Committee of the Chinese Communist Party (CCP).

"Every one of us on the Standing Committee (of the NPC) approves of and supports the party Central Committee's decision on amending the Constitution," he said.

But the speed at which the amendments - the first in 14 years - were made contrasted with the NPC's more deliberate approach to other reforms. For instance, where proposed reforms were in conflict with existing laws, the NPC would first call for preliminary trials, and delegates would then evaluate the results before deciding on whether to proceed with a wider roll-out.

Said Mr Zhang: "For reform measures requiring further exploration, we decided to either extend the trial period or launch new trials with a view to further refining the reform measures."

Mr Zhang, China's No. 3 leader and its top official for Hong Kong affairs, also highlighted as a major initiative two occasions when the NPC Standing Committee had "taken firm steps to uphold constitutional order in Hong Kong".

The first was in 2014, when it decided to allow Hong Kong voters to choose their chief executive, but on the condition that a nominating committee loyal to Beijing selects the candidates.

The second was the NPC's ruling on Hong Kong's Basic Law, or mini-Constitution in 2016 , which stated that legislators taking their oath of office have to do so "sincerely" and "solemnly" or face disqualification.

Beijing will resolutely deter and oppose any attempt at Hong Kong independence and safeguard the sanctity of China's Constitution and Hong Kong's Basic Law, Mr Zhang said to loud applause.

Setting out its work for this year, he said the NPC will formulate new laws governing foreign investment, e-commerce, and control of soil and solid-waste pollution, among others, while strengthening oversight of various ministries.

"We need to exercise oversight with greater intensity, ensuring it is proper and effective and produces real results," he said.