Image copyrightCarlos Jones/Oak Ridge National LaboratoryImage caption The Summit supercomputer is housed at the Oak Ridge National Laboratory in Tennessee. China has been pushed into third place on a list of the world's most powerful supercomputers.The latest list by Top 500, published twice a year, puts two US machines - Summit and Sierra - in the top two places.

The US has five entries in the top 10, with other entries from Switzerland, Germany and Japan.However, overall China has 227 machines in the top 500, while the US has 109.

Summit can process 200,000 trillion calculations per second.Both Summit and Sierra were built by the tech giant IBM.China's Sunway TaihuLight supercomputer, which this time last year was the world's most powerful machine, is now ranked at number three, while the country also has the fourth spot in the list.Sunway TaihuLight has a processing power of 93 petaflops, compared with Summit's 200.It was nudged out of second place by Sierra, which is in the Lawrence Livermore National Lab and has a processing power of 94 petaflops.

Supercomputers are typically large, expensive systems featuring tens of thousands of processors designed to carry out specialised calculation-intensive tasks, such as climate change studies, nuclear weapons simulations and weather forecasting.