Singapore has 21 billionaires, a record high for the city state, according to the latest Forbes rich list.

The number was 16 last year.

Robert and Philip Ng, sons of the late Far East Organization founder Ng Teng Fong, retained their top position on the list, with their estimated net wealth at 10.6 billion U.S. dollars, up from 9.2 billion U.S. dollars last year.

Kwek Leng Beng, chairman of City Developments, saw the biggest rise in his net wealth. His ranking also jumped to the second spot from number six. He has a net worth of 7.1 billion U.S. dollars, up from 2.4 billion U.S. dollars.

The Khoo family kept its number three spot, with a net worth of 6.7 billion U.S. dollars.

The combined net wealth of Singapore's 50 richest is 80 billion U.S. dollars.

Forbes said the list was compiled using shareholding and financial information. Unlike the Forbes billionaire rankings, the list includes family fortunes, including those shared among extended families.