British Prime Minister Theresa May is visiting Saudi Arabia looking to secure post-Brexit investment from the UK's biggest trading partner in the Arab world.

May arrived in the Saudi capital Riyadh on Tuesday with economic issues a "priority" on her trip.

Last month, May triggered Article 50 of the Lisbon Treaty, formally starting a two-year process of negotiations that will lead Britain to leave the European Union after 44 years.

May met Sarah al-Suhaimi, the head of the Saudi stock exchange, and Crown Prince Mohammed bin Nayef, the country's interior minister and first in line to the throne.

She is scheduled to meet King Salman on Wednesday.

May has said she is looking to use the "immense potential for Saudi investment to provide a boost to the British economy" during her trip to the region.

With Britain looking to strike new trade deals as it prepares to leave the EU, May has eyed longtime partners in the energy-rich Gulf states.

Saudi Arabia is Britain's largest trading partner in the Middle East, with exports of more than $8bn in British goods and services to the country in 2015.

Riyadh is also looking at boosting its foreign investments as part of a long-term plan known as "Vision 2030", which aims to diversify the economy and reduce dependence on oil revenues.

Britain voted to leave the EU last June, after a campaign that divided the country. In a close result, 52 percent voted for Brexit, while 48 percent wanted to stay in the EU.

May has promised to take Britain out of the EU single market but negotiate a deal that keeps close trade relations with Europe, as she builds "a strong, self-governing global Britain" with control over its own borders and laws.