RABAT/ABU DHABI (Reuters) - Rescuers on Sunday were searching a Moroccan hillside lake for the boss of the world's largest sovereign fund, the Abu Dhabi Investment Authority (ADIA), two days after his plane crashed into it.

The aircraft of Sheikh Ahmed bin Zayed Al Nahayan, the younger brother of the ruler of Abu Dhabi, who is also president of the United Arab Emirates, crashed into a reservoir 10 km (6 miles) south of the Moroccan capital Rabat on Friday.

"The search is still going on, that is all that I can tell you," Moroccan Communications Minister Khalid Naciri said.

Sheikh Ahmed is in his early 40s and was ranked No. 27 on Forbes list of the world's most powerful people last year.

His sovereign wealth fund is believed to have assets of around $500 to $700 billion, ranging from Citigroup bonds to a stake in Britain's Gatwick airport to residential property in major cities.

Few details have emerged about the accident except that the pilot of the craft was rescued after it crashed near Sidi Mohamed Ben Abdallah Dam.

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

Dozens of police on Sunday blocked roads leading to the lake, which is set in green, rolling hills. Several black Mercedes-Benz cars with diplomatic licence plates swept through a police blockade down the road leading to the royal family's palace. Moroccan government vehicles followed.

UAE officials have made no comment since a statement on Friday reporting the crash. In the conservative Gulf region, health concerns about royal family members are treated with great deference and sensitivity and officials are rarely willing to comment before announcements from the ruling families.

"The suspense is unbearable, at least we should know whether he is found and about his condition," said a senior Abu Dhabi businessman on condition of anonymity.

ADIA is viewed as the world's largest state-run investor, 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, like the organisation he leads, has shunned the media spotlight. He 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.

The fund has rarely given details of its investment strategy or investments. In its first detailed report published in March, ADIA said it aimed to be more transparent. It also said it returned 6.5 percent on an annualised basis over a 20-year period as of December 31, 2009 and 8 percent over a 30 year period.

The chairman of ADIA is Sheikh Khalifa Bin Zayed al-Nahayan, ruler of Abu Dhabi and President of the UAE.

An ADIA spokesman could not be immediately reached for comment.