US Pacific Fleet Commander Admiral Harry Harris made the comments in a speech in Australia on Tuesday night.
He said by pumping sand on to coral reefs and adding concrete, China had created "over 4sq/km (1.5 sq miles) of artificial landmass".
China has overlapping claims with neighbours in the South China Sea.
It has been reclaiming land in contested waters - something it said last year was "totally justified" as it had "sovereignty" over the area .... http://www.bbc.com
