China marked its first national Constitution Day on Thursday with readings at schools across the country, activities promoting the rule of law, and the blocking of protests at Tiananmen Square.

The National People's Congress, China's rubber-stamp legislature, last month designated December 4 as National Constitution Day to promote the document adopted in its current form on that date in 1982.

State broadcaster China Central Television showed footage of judicial employees swearing an oath to the constitution at Beijing's high court.

On Wednesday, President Xi Jinping said China's constitution "guarantees the socialist path with Chinese characteristics", according to the state-run Global Times newspaper.

Schools across China were to hold readings of the constitution, according to an education ministry directive, and tables were set up on some central Beijing streets with posters and materials promoting the document.

Yet at Tiananmen Square, the vast public space in the heart of the city, citizens seeking to protest were blocked by police from doing so.

A middle-aged man was stopped and got into an altercation with officers at a security checkpoint after he attempted to enter the square with briefcase containing a pile of flyers.

One officer videotaped as another yelled at the man, grabbed him by the front of his coat and thrust him into a chair.

Half a dozen people were also seen being bundled by police into a van at the centre of the square on Thursday morning, although it was unclear whether they were seeking to demonstrate.

Metres away from the square, an electronic billboard -- adorned with at least three CCTV cameras -- carried messages promoting the new commemoration, previously known as Legal Day.

"December 4 is National Constitution Day and National Day of Promoting the Legal System," it read. "Promote the spirit of the Constitution, establish constitutional authority."

- 'Leadership of the party' -

Article 35 of China's constitution states: "Citizens of the People's Republic of China enjoy freedom of speech, of the press, of assembly, of association, of procession and of demonstration."

Yet the Communist Party of China (CPC) maintains a tight grip on expression, with protests regularly quashed and human rights lawyers and activists coming under increasing pressure since Xi took power last year.

Jean-Pierre Cabestan, a specialist in China's political and legal systems at Hong Kong Baptist University, said that the party's renewed promotion of the constitution is in part an effort to address pressure being exerted by the nascent rights defence movement within China.

In a December 2012 speech Xi emphasised the primacy of the Constitution, but Cabestan noted that lawyers and other reformists who viewed his remarks as a call for greater judicial independence misinterpreted the leader's words.

"Some reformists and legal experts jumped on that occasion to launch this constitutionalism debate and try to push the limits of the system," he said. "They failed, and the result has been the arrests of a number of activists."

A conclave of top party leaders in Beijing last month, Cabestan added, made clear that "the Constitution is under the leadership of the party".

China's state-run media on Thursday ran a series of articles promoting the newly-declared Constitution Day.

The official Xinhua news agency published an article featuring interviews with people named Xianfa, the Chinese word for "constitution".

In an editorial, the Global Times wrote that the "Constitution clearly states that the (party) is the leader of this country, but it also endows Chinese people with free speech. If some people take advantage of their rights to speak freely, circulating ideas to topple the CPC's leadership, how can we define the nature of their actions?"

It called for a court ruling to "to set a precedent on what is constitutional" -- but said the actions of Liu Xiaobo, the jailed dissident who co-authored Charter 08 calling for multi-party democracy, were "nothing but defiance of the Constitution".