Events to mark the occasion began across the kingdom on Wednesday and will carry on until Sunday.
Saturday will be an official holiday for the private and public sectors, the Ministry of Human Resources and Social Development has announced.
Schools and universities will be given an additional day off on Sunday.
A military parade was held in Riyadh on Thursday, with the participation of the Ministry of Interior.
The government has organised a military march and air shows in cities including Riyadh, Jeddah, Taif, Al Baha, Tabuk, Abha, Dhahran, Al Jawf, Al Ahsa, Khamis Mushait, Al Khobar and Dammam.
The 93rd National Day celebrations aim to reflect the "pride in the kingdom's present and the achievements it has achieved to build the future in accordance with Saudi Vision 2030", the Saudi Press Agency reported.
Roads, billboards, malls and offices across the kingdom have been decorated with the Saudi flag and traditional motifs.
"Today we celebrated with a beautiful Saudi dance and musical performance in our office. We had Saudi coffee, dates and desserts during the afternoon," said Nabil Alfaiz, 36, a marketing executive in Riyadh.
"I plan to celebrate with the family as my wife and children also have a National Day holiday."
'First Ronaldo, now Neymar'
As Saudis and residents celebrate National Day, some have reflected on major milestones reached during the past year.
Saudi Pro League clubs have attracted global talent to the kingdom – capturing the imagination of supporters at home and abroad.
"This year has been very special to me as I am a football fan. First [Cristiano] Ronaldo joined us and this year Neymar. I am a big fan of them and very happy to celebrate this year as we one of the best football leagues in the world," said Amir Hashim, 15, who lives in Jeddah.
The theme of this year's celebrations is "This is Our Home".
“Our dreams have not stopped since the foundation of this kingdom and we will work to achieve them as long as we live. Let’s celebrate our accomplishments,” said a statement on the National Day website.
People have thronged to malls to take advantage of sales and find items to help them mark the occasion.
"The malls are full of life as you can hear the national songs being played all day. Malls are crowded as schools and public offices have holidays," said Nahla Eman, 37, a Saudi saleswoman in Jeddah.
Another saleswoman, Umm Talal, said her shop green abayas have been popular this year.
"We ordered more stock to fill the growing demand. It is a busy season and full of activities," she said.
Military and biker parades
Military events, a biker parade and an arms exhibition have been among the nationwide celebrations.
"I went on Wednesday to see the air show on the Corniche with my sisters," said Maha Abdullah, 28, in Jeddah.
"We love coming out on National Day. We dress up in green dresses and abayas. It's good to see all the cars decorated with flags and people enjoying this day to celebrate our nation and leadership."
The eastern and western fleets of the Royal Saudi Navy will participate in the National Day celebrations in Jeddah.
The National Day celebrations honour "the endeavours and efforts that came together to achieve successful initiatives that benefit the citizen and the resident", the General Entertainment Authority said.
Diana Wijaya, an Indonesian resident in Al Khobar, said she marks the day every year with friends.
“We watch the air show and fireworks," she said.
"Sometimes we go around Al Khobar and try new coffee stores.
“We love Saudi Arabia so much, we want to celebrate and share our happiness for the good times we had here. People passing by were recording us and they’re all happy to see what we’re doing."
Schools across the kingdom planned to hold National Day activities, before closing for the long weekend.
"It was great to see all the kids dressed up in the colours of the national flag. We bought them headbands, thobes and flags to enjoy the celebration with friends," said Canadian citizen Amina Mudassir, 40, who lives in Jeddah.
"Saudi National Day is equally celebrated by citizens and residents. We are so happy to be living in such a safe and prosperous nation."