Saudi Arabia and Oman on Tuesday opened the first direct land crossing between the two Gulf neighbours, a joint statement said.

"The two sides welcomed...the opening of the 725 km Omani-Saudi road, which will contribute to the smooth movement of citizens of the two countries and the integration of supply chains," it said.

Saudi Arabia's Public Investment Fund (PIF) will invest five billion dollars in Oman, Saudi state news agency said, after Saudi Crown Prince Mohammed bin Salman visited as part of a Gulf tour.

Omani and Saudi firms has signed 13 memoranda of understanding (MoU) valued at $30 billion, the Saudi state news agency (SPA) reported.