China sees "enormous potential" in Saudi Arabia's economy and wants more cooperation, the Chinese government's top diplomat says, as Saudi Crown Prince Mohammed bin Salman begins a two-day trip to Beijing.

The Saudi delegation, including executives from Aramco, arrived on Thursday on an Asia tour that has already seen the kingdom pledge investment of $US20 billion in Pakistan and additional investment in Indian refining.

The crown prince will also meet President Xi Jinping, who has made stepping up China's presence in the Middle East a key foreign policy objective.

"All countries in the world have the right to develop, and Saudi Arabia is an emerging market country with enormous potential," the ministry paraphrased Foreign Minister Wang Yi as saying.

Saudi Aramco, the world's top oil exporter, will sign a pact to build a refinery and petrochemical project in the northeastern Liaoning province in a joint venture with China's defence conglomerate Norinco.

The investments could help Saudi Arabia regain its place as the top oil exporter to China, a position Russia has held for the last three years.

China has had to step carefully in relations with Riyadh, since Beijing also has close ties with Saudi regional foe Iran.

On Wednesday, Xi told the speaker of Iran's parliament that China's desire to develop close ties with Iran would stay unaltered.

China is also wary of criticism from Muslim countries about its camps in the heavily-Muslim western region of Xinjiang.

Wang said both countries face the threats of terrorism and extremism, and should strengthen cooperation to safeguard security and stability.