China's defense budget is set to double by 2015, which will be more than the combined spend of all other key defense markets in Asia Pacific, a global think tank has said.

According to IHS, China’s defense spending will hit $238.2 billion in 2015, which will be reaching around four times Japan’s defense budget, the region’s next biggest spender.

Beijing has been able to devote an increasingly large portion of its overall budget towards defense and has been steadily building up its military capabilities for more than two decades, said Rajiv Biswas, Asia-Pacific chief economist for IHS Global Insight.

The growth in China's defense budget, which averaged 12 percent annually from 2000 to 2009, will benefit from the projected surge in the gross domestic product of Asia's largest economy in the next three years.

Apart from China and Japan, the report also tracks the military spending of India, South Korea, Australia, Taiwan, Singapore, Indonesia, Pakistan, Thailand, Malaysia, Vietnam and New Zealand.

China’s investment will race ahead at an eye watering 18.75 percent, leaving Japan and India far behind. But this isn’t a three horse race. Taiwan’s rate of investment means it will have overtaken Singapore in terms of defense spend by 2015, while Vietnam and Indonesia are also forecast to increase defense spending at a rate that exceeds GDP growth, said Paul Burton, senior principal analyst, IHS Jane’s Defense Budgets. China’s rise is not the only motivator. There are a number of lingering security issues, driven by competition for untapped natural resources, that are prompting many states to increase their defense to GDP ratio, he added.

According to IHS Global Insight's Asia-Pacific head Sarah McDowall, the U.S. government's renewed Asia-Pacific focus is helping fuel China's expansion of its defense budget.

China's spending is beginning to close the gap with the U.S., which until recently accounted for almost 50 percent of the world's defense spending. In the coming years, IHS Jane's expects the U.S. military budget to shrink, but remain three times as large as that of China in 2015.