Rescuers combing a Moroccan hillside lake for a missing member of Abu Dhabi's ruling family who is chief of the Abu Dhabi Investment Authority (Adia), a major sovereign fund, have narrowed their search zone, state media said on Tuesday.

The glider of Sheikh Ahmed bin Zayed Al Nahayan crashed near the Sidi Mohamed Ben Abdallah Dam south of the Moroccan capital Rabat on Friday.

The pilot was rescued and a search launched for Sheikh Ahmed, ranked No. 27 on Forbes list of the world's most powerful people last year. He is the younger brother of the ruler of Abu Dhabi, who is also president of the UAE.

"The search area, which was wide and sprawling, has been narrowed ... to focus the current search on smaller, more defined areas," the Emirati state news agency WAm quoted a statement from the search team as saying.

Teams from five countries were searching for Sheikh Ahmed.

Separately, Wam reported that Abu Dhabi had postponed two major cultural events as the search for the missing sheikh continued.

"We hope rescuers succeed in their mission to find Sheikh Ahmed and bring him back home safe," said Mohammed Khalaf Al Mazrouei, director general of the Abu Dhabi Authority for Culture and Heritage.

UAE officials have made little comment on Sheikh Ahmed's fate since the crash. In the conservative Gulf region, news about ruling family members are treated with great deference and sensitivity, and officials are rarely willing to comment before announcements from the ruling families.

Sheikh Ahmed's sovereign wealth fund Adia is believed to have assets of around $500 to $700 billion, ranging from Citigroup bonds to a stake in Britain's Gatwick airport.

Residents of the area said the sheikh, in his early 40s, was a regular visitor and that the Abu Dhabi ruling family had a palace overlooking the reservoir, which was swollen due to high rainfall and estimated to be about 60 meters deep.

Adia is among the world's top state-run investors, funnelling funds from the emirate's oil exports into stocks and bonds overseas from its headquarters in a gleaming skyscraper on the island city's shoreline.

Sheikh Ahmed is the son of the founder of the seven member UAE federation, Sheikh Zayed bin Sultan al-Nahayan, and worked as a European equities analyst at Adia for six years before becoming its boss. – Reuters