Media playback is unsupported on your device Media caption Jim Yong Kim, head of the World Bank: "A growing Japan is good for everybody"

Japan's stock market has hit its highest level in almost five years, after a central bank stimulus plan raised hope of economic revival.

The main Nikkei 225 stock index climbed as much as 4.7% to 13,225.62, its highest since August 2008.

The Bank of Japan said on Thursday it would double the country's money supply to spur growth and halt falling prices.

The step was much bigger than expected and signalled a more aggressive approach towards driving growth.

After a day of heavy trading, the Nikkei closed up 1.58%, or 199.10 points, at 12,833.64.

The president of the World Bank, Jim Yong Kim, welcomed the Bank of Japan's commitment to "doing what it takes" to restart growth.

"The critical thing is, a growing Japan is good for everybody. It is very important for the region, but it is important for the entire world," he told the BBC.

Analysis Market reaction to the Bank of Japan's new stimulus measures show that Haruhiko Kuroda's bold moves were definitely more than investors expected. Some have praised Mr Kuroda - former president of the Asian Development Bank - for his understanding of how global markets and investors would react when it comes to monetary policy. The recent hype of what is known as Abenomics - Prime Minister Shinzo Abe's economic policies - may also remind many of what happened under former PM Junichiro Koizumi, whom Mr Abe served as chief cabinet secretary. Mr Koizumi promoted aggressive structural reforms which also resulted in a sharp fall in the Japanese yen. There are those who warn that at the time the weakening yen didn't help Japan's exporters longer term. And, according to the latest trade figures, exports fell 16% in February from the month before, indicating that the weak yen has yet to help companies to sell more products abroad.

Yen factor

By pumping more money into the system, Japan is hoping to promote price growth, ending a cycle of deflation, recession and sputtering economic recovery.

At the same time, it is also seen as an attempt to weaken its currency and boost exports.

The Japanese yen has declined 4.5% against the US dollar in the past two days, and more than 5% against the euro.

Analysts said the yen was likely to remain weak in the coming months.

"The big party we are having in the markets now is, of course, the financials. Banks are getting more money for free, utilities with big investment projects are getting zero cost capital now," said Martin Schulz from Fujitsu Research Institute.

"The big story, and the lasting story, will be the exporters. A weaker yen helps the exporters to earn money with Japanese technology in Asian markets in particular."

Global shift?

On Thursday, the Bank of Japan embarked on what some are calling a new era of monetary easing.

It will increase its purchase of government bonds by 50tn yen ($520bn; £350bn) annually, the equivalent of almost 10% of Japan's gross domestic product, or total economic output.

The new BOJ governor Haruhiko Kuroda defended the size of the stimulus saying the government's inflation target of 2% would remain out of reach if the central bank continued its incremental steps.

He said he would "do whatever it takes" to drive growth.

However, analysts say Japan's new direction is likely to provoke a reaction from their main competitors.

Asset bubbles?

The central bank's moves to buy additional bonds is an attempt to keep long-term interest rates low.

The bank hopes that pumping money into the system will make borrowing cheap and encourage consumers and businesses to spend.

The central bank has also said that it would buy riskier assets such as exchange-traded funds and real estate trust funds.

While such moves may help halt years of falling prices, some analysts have warned that there is a risk that so much liquidity in the markets may trigger an artificial rise in asset prices.

"We think there is a risk of a bubble," said Hiroshi Shiraishi, senior economist at BNP Paribas Securities.

"If these types of asset purchases are going to work, then they work by distorting asset markets."

However, on Friday Mr Kuroda, sought to allay those fears, saying the bank will keep a close eye on the markets.

"I don't think there's a bond or stock market bubble now and I don't see one emerging any time soon," Mr Kuroda told Japan's lower house of parliament.

"But we will be vigilant of the risk."