The kingdom has ambitions to double the size and population of its capital city with total investments of some $800 billion under its Vision 2030 plan to modernise the Gulf Arab state and diversify the economy to wean it off oil export revenues.

Fahd Al-Rasheed, president of Riyadh's royal commission, said the $8 billion bill to build the Expo site paled in comparison to the $400 billion of construction investment currently in the city of eight million people.

"We are building the largest transport network in the world, we are building the largest airport in the world, and over 30 mega-projects as we speak are being constructed, so the city is a hive of economic activity," Al-Rasheed told reporters on the sidelines of the World Economic Forum in Davos, Switzerland.

Should Riyadh win Expo hosting rights it would be ready, but the build-up, which includes an additional 120,000 hotel rooms by 2030, was needed regardless to meet tourism goals, he said.

The host country for the 2030 Expo is expected to be selected in November. Riyadh is competing with Italy's Rome, South Korea's Busan and Ukraine's Odesa.

Saudi Arabia has also pushed through social reforms to modernise the conservative country, the birthplace of Islam, including lifting a ban on women driving and permitting public entertainment like concerts.

Asked if alcohol would be allowed in Riyadh by 2030, Al Rasheed said: "No, but I think you can ... consider it a wellness detox."

On religious freedom in a state that does not allow non-Muslims to practice their faith publicly, he said there was "a level of openness happening".

The kingdom has faced Western criticism over its human rights record, which came under intense scrutiny after the 2018 murder of journalist Jamal Kashoggi by Saudi agents.

If Saudi Arabia wins its bid it would be the second Arab country to host Expo after the United Arab Emirates. Last year neighbouring Qatar hosted soccer's World Cup, which drew sharp criticism over Doha's human rights record.