Sakai, one of Japan's top hopes for the London Olympics in 2012, broke the previous mark of 56.51 set by Natalie Coughlin of the United States.

'Of course, I set out to set a new world record. I'm very surprised that I did and I'm very, very happy about it,' said a jubilant Sakai.

'I tried to swim as aggressively as possible in the first half and tried to be patient in the latter. I did as I planned. This is my last race as a high school student and I really wanted to set my personal best to finish with.

'From now on, I'm going to aim for the national championships in April and qualify for the world championships.'

The Chinese duo of Gao Chan and Zhao Jing finished second and third in 56.96 and 57.08, respectively. -- AFP