Saudi Arabia's King Salman has ordered the reopening of the border with Qatar to facilitate the annual Haj pilgrimage, state media said on Thursday, in the first signs of a thaw after the region's worst diplomatic crisis in years.

The Salwa border crossing had been shut after regional kingpin Saudi Arabia as well as Egypt, Bahrain and the United Arab Emirates severed diplomatic and trade ties with Qatar on June 5, accusing the emirate of fostering Islamist extremist groups.

The announcement to reopen the border for Qatari pilgrims came after Saudi Arabia's powerful Crown Prince Mohammed bin Salman received an envoy from Doha, according to the official Saudi Press Agency, in the first public high-level encounter between the nations after the crisis erupted.

The king has permitted “the entry of Qatari pilgrims to the Kingdom of Saudi Arabia through Salwa border crossing to perform Haj, and to allow all Qatari nationals who wish to enter for Haj without electronic permits”, a statement on SPA said.

He also ordered that private jets belonging to Saudi Arabian Airlines be sent to Doha airport “to bring all Qatari pilgrims on his expenses”.

The crown prince emphasised the “historical relations between Saudi and Qatari people” after his meeting with Qatari Sheikh Abdullah bin Ali bin Abdullah bin Jassim al-Thani, the statement added.

Last month, Saudi Arabia had said that Qataris wanting to perform this year's Haj would be allowed to enter the kingdom, but imposed certain restrictions including that those arriving by plane must use airlines in agreement with Riyadh.

Qatari authorities had subsequently accused Saudi Arabia of politicising Haj and jeopardising the pilgrimage to Mecca by refusing to guarantee their pilgrims' safety.

Some observers cautioned that the diplomatic crisis was far from over despite the apparent bonhomie.

“This is a goodwill gesture towards the Qatari people and not a breakthrough with the Qatari govt,” Ali Shihabi from the Washington-based think tank Arabia Foundation said on Twitter, referring to the reopening of the border.

Saudi Arabia and its Arab allies shut down air, maritime and land links with Qatar, and imposed economic sanctions, accusing Doha of supporting “terrorists” and of being too close to their regional nemesis Iran.

Qatar denied the allegations and denounced what it called a “blockade” aimed at bringing the wealthy emirate to its knees.

The tiny emirate with a population of 2.6 million, 80 per cent of them foreigners, ranks as the world's richest on a per capita basis, according to the International Monetary Fund.

It holds a staggering $330 billion in a sovereign wealth fund, with assets heavily invested abroad.