Hundreds of women thronged a sports stadium for the first time to mark Saudi Arabia's national day on Saturday, celebrated across the conservative kingdom with concerts, folk dance and fireworks displays.

The presence of women at the King Fahd Stadium in Riyadh for a pageant operetta marked a departure from previous celebrations in the Gulf kingdom, where women were effectively barred from sports arenas by strict rules on segregation of the sexes in public.

Women were allowed to enter the stadium, a previously male-only venue used mostly for football matches, with their families and were seated separately from single men to watch a play on Saudi history.

"It is the first time I have come to the stadium, and I feel like more of a Saudi citizen. Now I can go everywhere in my country," said 25-year-old Sultana, green and white flags painted on both cheeks as she entered the complex with her girlfriends.

"God willing, tomorrow women will be permitted bigger and better things, like driving and travel."

The whole town is in green! Saudi National Day... check out Riyadh’s Kingdom Tower light show! pic.twitter.com/2ed51FrEdo — HAROLD (@imSimply_HAROLD) September 23, 2017

Ultra-conservative Saudi Arabia has some of the world's tightest restrictions on women and is the only country where they are not allowed to drive, despite government reforms aimed at boosting female employment.

Under the country's guardianship system, a male family member - normally the father, husband or brother - must grant permission for a woman's study, travel and other activities.

But the kingdom appears to be relaxing some norms as part of its "Vision 2030" plan for economic and social reforms conceived by powerful Crown Prince Mohammed bin Salman.

The General Entertainment Authority, the government agency organising the National Day festivities, expects about 1.5 million Saudis to attend events in 17 cities over four days.

Vision 2030 reforms are intended to capture up to a quarter of the $20b currently spent overseas by Saudis, who are accustomed to travelling abroad to see shows and visit amusement parks in nearby tourist hub Dubai or further afield.

This weekend's events are free to the public.

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The national day celebrations coincide with a crucial time for Saudi Arabia, which is in a battle for regional influence with arch-rival Iran, bogged down in a controversial military intervention in neighbouring Yemen and at loggerheads with US Gulf ally Qatar.

Iconic buildings in Riyadh were bathed in green light and stereos blared patriotic songs as revellers raced through the streets in cars bedecked with the national flag.

With drumming and poetry, traditional sword dancers celebrating the warrior tradition of Saudi Arabia strode through Tahlia Street, an upscale shopping strip in the heart of Riyadh.

The operetta at the stadium told the story of the founding of the modern Saudi state by Ibn Saud, King Salman's father, in 1932 following a series of territorial conquests and before the discovery of oil opened the way to making the new kingdom the world's top oil exporter.

"On this great occasion, we feel that the kingdom has become an important state with a pioneering role at the regional and international levels," Prince Mohammed said in a speech earlier cited by the official Saudi Press Agency.

The 32-year-old prince is set to be the first millennial to occupy the throne in a country where half the population is under 25, although the timing of his ascension remains unknown.

Already viewed as the de facto ruler controlling all the major levers of government, from defence to the economy, the prince is seen as stamping out traces of internal dissent before any formal transfer of power from his 81-year-old father, King Salman.

Authorities this month arrested about two dozen people, including influential clerics, in what activists decried as a coordinated crackdown.

Analysts say many of those detained are resistant to Prince Mohammed's foreign policy, which includes the boycott of Qatar, as well as some of his reforms, dubbed Vision 2030, which include privatising state assets and cutting subsidies.

"On this cherished anniversary of the unification of our dear country, the kingdom of Saudi Arabia, we assert its effective and influential status," the prince said in his speech.

"The kingdom is an active member in the G20, the world's strongest 20 economies, and is keen to achieve the kingdom's Vision 2030 that represents the beginning of a new phase of hard work for a better future, with the same Islamic values."

The kingdom's General Entertainment Authority is hosting 27 events across 17 cities to celebrate national day, including concerts, laser shows and firework displays.