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China has the world's most powerful supercomputer for the third time in a row as the country once again ups its presence in the global top 500.

Tianhe-2 was top of the twice-yearly list that keeps tabs on supercomputer development and growth.

Since the last list, China had 20% more supercomputers in the top 500, while US representation went down 15%.

However, the US still dominates the chart with 233 computers making the latest tally.

China had 76, up from 63 in the last count. This is almost as many as the UK (30), France (27) and Germany (23) combined.

The full list will be published on Monday at a conference in Leipzig, Germany.

The list is a widely-recognised barometer of the state of worldwide supercomputing. It has been published twice yearly since 1993.

All the computers are measured against the same criteria - a benchmark first devised in 1979 but since improved as computing has become ever more sophisticated.

Such is the immense power of the supercomputers, their computational ability is measured in petaflop/s - quadrillions of calculations per second.

The top performing computer, Tianhe-2, had its power measured at 33.86 petaflop/s (quadrillions of calculations per second). It has been just five years since IBM's Roadrunner became the first computer to break the 1 petaflop/s mark. That machine was shut down in 2013 due to excessive power consumption.

The entire top 500 list of supercomputers combined offered 274 petaflop/s.

Tianhe-2 is owned by the Chinese government and operated by the National University of Defence Technology. It is used as a "research and educational" tool.