The congress will select the members of the influential Politburo and Central Committee, the key decision-making bodies governing the landlocked but resource-rich country.

It comes as Laos assumes the year-long chairmanship of the ASEAN regional bloc that will see a cascade of diplomatic meetings and open the cloistered, tightly-controlled nation to greater scrutiny.

Launching the congress, Prime Minister Thongsing Thammavong, lauded Laos’ decade-long boom which has seen an average annual growth rate of 7.4 per cent.

Highlighting a vision for lifting the country out of poverty, he told delegates that the “difference between city and countryside will narrow... human resources will develop, citizen's rights will be protected, the environment will be preserved”.

Laos faces a plethora of major environmental challenges, many the result of Chinese-built megadams, mining operations and massive deforestation.

The nation has one of the fastest growing young populations in the world with around 70 per cent of its 6.7 million people under 30.

Nonetheless its leaders almost all exclusively hail from the revolutionary era and are in their seventies overseeing a tightly-controlled nation with a poor human rights record.

The last party congress, held in 2011, opted for stability with Choummaly Sayasone retaining the top party position of secretary general.

But Choummaly is widely expected to retire and observers expect the congress to play host to political manoeuvres by his allies and opponents.

Experts on the secretive state said that Vice President Bounnhang Vorachith is the most likely successor to Choummaly.

That could leave Prime Minister Thongsing, often seen a rival to Choummaly, on the sidelines.

One Western official, requesting anonymity, said that old guard were losing some of their grip, particularly within the Central Committee which sits under the Politburo.

“There's a transition going on between the last revolutionary veterans and a younger generation of cadres, many of whom went to universities in Vietnam or the Soviet Union and therefore have a somewhat more international mindset,” the official said.

Laos’ communist rulers heavily restrict foreign media access to the country.

Western media have not been granted permission to observe the congress, though some journalists from China and Vietnam usually attend.

The Foreign Mass Media Division said that “due to the short time of preparation” for the five-yearly event, it was unable to facilitate foreign media to cover the congress.