LONDON (REUTERS) - Gold, Switzerland's franc, Japan's yen, top-rated government bonds, and even bitcoin - investors have dashed for havens and alternative assets this week as anxiety grows about trade wars, US-Iran tensions and negative interest rates.

Although world stocks and bonds remain near record highs thanks to promises of ever more central bank largesse, the sudden dash for these financial bunkers shows all is not as calm as a cursory reading of headline indexes suggests.

Fears of a global trade war have been simmering for over a year but the latest standoff between Washington and Beijing may come to a head at the G-20 summit in Japan this weekend. New US tariffs on Chinese imports could kick in next month if there's no progress between the two sides.

Military tensions between the United States and Iran have also gone up several notches after Tehran's downing of an unmanned American drone last week and claims that US retaliation was stopped at the last minute. A fresh wave sanctions on Iran's leaders and a war of words between the two sides have followed.

The trade and geopolitical worries are compounding investor concern about a looming global economic downturn and whether central banks are easing policy again quickly enough to offset it. Even if they are, the expanding universe of bonds with a negative yield - effectively penalising investors for holding them - is unnerving for many.

"It comes at the worst possible moment because we are late-cycle, we are worried about global growth, and the US are fighting on many fronts," said Frederic Ducrozet, a strategist at Pictet Wealth Management, referring partly to the trade conflict between the US and China.

He said that under normal circumstances, the reaction to the dispute in the Middle East would have been confined largely to oil prices. But because of worries over global growth and the tail risk from trade negotiations, flows are being directed instead into safe assets.

"This Iran conflict is the cherry on the cake," said Ducrozet.

Nowhere has the move been more marked than in gold. The precious metal struck a six-year high of 1,438.63 on Tuesday, up a whopping 11.2 per cent over the past month. "Safe" currencies the Japanese yen and Swiss franc are around 2 per cent and 2.7 per cent higher respectively over the same period.

Ducrozet even pointed to bitcoin's resurgence - up 40 per cent over the last month - as possibly partly driven by the search for alternative investments.

The promise of fresh stimulus from the world's top central banks has fuelled an all-inclusive rally in public assets, with equities and bonds rising in tandem. That is unsettling for portfolio managers who use the more typical inverse relationship between stocks and bonds to balance and insulate their funds.

The fear is that if they correlate on the way up, they will do so on the way down - hence the search for more alternative assets to diversify portfolios.

"It seems that the world is so awash with money, that it is creating financial asset price inflation wherever you look," ING economist Robert Carnell said in a note last week. "Something is wrong here. Moreover, the likelihood that if and when this is realised, the positive correlation between all assets means that my portfolio diversification will all count for nothing is rather disturbing."

What's more, there are growing worries that central banks under pressure from politicians and markets alike are finding it harder to read the signals on inflation and growth due to the lack of visibility on policy and trade.

On Monday, Us President Donald Trump again criticised the Fed for not cutting interest rates fast enough saying the world's most important central bank "blew it" and didn't know what it was doing.

On Tuesday, Fed chief Jerome Powell defended the central bank's independence from Trump and financial markets, both of which seem to be pushing for aggressive rate cuts, in remarks at the Council on Foreign Relations in New York.

"The Fed is insulated from short-term political pressures," said Powell. Asked later about the possibility of disappointing markets by not delivering a cut, Powell added, "We're not in the business, really, of trying to work through short-term movements in financial conditions. We have to look through that."