The presence of women at the King Fahd stadium marks a departure from previous celebrations in the Gulf kingdom where they are effectively barred from sports arenas by strict rules on public segregation of the sexes.
Women were allowed to enter the stadium, a previously male-only venue used mostly for football matches, with their families and seated separately from single men to watch a musical show and a play on Saudihistory.
"We hope in the future that there will be no restrictions on our entrance to the stadium," Um Abdulrahman, awoman from the northwestern city of Tabuk, told AFP.
"For many years ago I have hoped that women will be given the same rights as men."
As a swell of enthusiastic women cheering swept through the stadium, with a few wearing colourful wigs on top of their veils, some Saudi men on social media lauded their participation as a "historic" moment.
"Looks like women bought all the tickets!" one Saudi man quipped on Twitter.
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 ambitious 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.
Drums, Poetry, Dance
The national day celebration coincides 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 inneighbouring Yemen and at loggerheads with fellow 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 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 around 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 aggressive foreign policy that includes the boycott of Qatar as well as some of his bold 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.
Saudi chefs in the Red Sea city of Jeddah broke the Guinness world record for baking the biggest marble cake -- with green icing -- to mark national day, the government said.
Saudi Arabia has cautiously begun introducing entertainment, including music concerts, despite opposition from hardliners in the kingdom, where public cinemas and theatre are banned.
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