Bitcoin and cryptocurrencies aren't the only bubble which investors should be worried about.

It's certainly the bubble getting the most attention this week, but people should also be careful of risks in the property and stocks markets, according to a report by Danish investment bank Saxo Bank.

"The length and extent of some of these bull markets may conceal just how far from fundamentals these assets have drifted," the bank's chief economist Steven Jakobsen said.

"The crypto bubble may be the most visible due to the high volatility and performance seen in 2017."

But how does one spot a bubble?

A bubble is "the situation created when prices go super-exponential" and causes a "departure from fundamentals", he said.

Another characteristic is that it's driven by "pure speculation" as "traders are buying and selling without even considering the fundamental value of the asset".

However, he warned this is followed by an eventual "sudden sharp decline when the bubble bursts".

Cryptocurrency's moment of truth

The entire cryptocurrency market plunged on Wednesday, amid fears of a major regulatory crackdown in South Korea.

It was a sea of red, with the big players bitcoin, Ethereum and Ripple dropping by more than 20, 25 and 40 per cent respectively.

Bitcoin's value even sunk below $US10,000, which is almost half the record price it reached one month ago — $US19,343 in mid-December, according to Coindesk.

Traders saw an opportune moment to "buy when it's low", and have since driven bitcoin's volatile price back to $US11,465 at 1.15pm AEDT.

Jacob Pouncey, Saxo Bank's crypto analyst, said 2018 "will be a make-or-break year for the burgeoning crypto[currency] asset market".

His prediction is that most cryptocurrencies (out of the 1,400 out there) will fail.

Furthermore, there are parallels that can be drawn between cryptocurrencies and the dot-com boom in the late 1990s.

"At the peak of the dot-com era, over 100 companies had changed their name," Mr Pouncey said.

In a similar vein, companies like beverage maker Long Island Iced Tea Corp have capitalised on the current "crypto bubble" by renaming itself "Long Blockchain Corp", which saw its share price skyrocket in December.

Former photograph giant Kodak did something last week, by launching KODAKCoin, which drove up demand for its shares.

The consequences will be dire for the cryptocurrency market in the event of a crash.

"If the market crashes, regulators will lash out at those involved and hinder the growth of the technology with burdensome red tape that could set the industry back years," Mr Pouncey said.

But its impact would not have much of an impact on the wider economy, according to Capital Economics.

The dangers of property

The most risky bubble is arguably not bitcoin or its rivals, but the property market.

"From a macroeconomic perspective, property bubbles tend to be the most dangerous because they affect such wide portions of the population," said the bank's head of macro analysis, Christopher Dembik.

"It will lead to a huge loss of wealth for homeowners who in many cases will not be able to afford their mortgage payments."

He identified the riskiest property markets to be Australia, London, Hong Kong, Sweden, and Norway — where housing prices kept rising despite the global financial crisis.

Australia's household debt to income ratio is around 200 per cent, and tipped to grow further.

However, investors may feel comforted knowing there's always someone in a less fortunate situation.

The authors of the report stated Australia's housing bubble has been going on for 14 years, with properties appreciating by 108 per cent — and average home prices 6.6 times higher than the annual median household income.

In contrast, London property has shot up 380 per cent in 21 years, with average home prices 12 times higher than typical household incomes.

Hong Kong's prospective buyers were found to be in an even worse position — with a 450 per cent rise in values, and home prices 18 times higher than average incomes.

What's behind the rampant rise in property prices is "accommodative monetary policy and excess liquidity," Mr Dembik said.

In other words, too much money being lent very low interest rates which makes it all too easy for people to borrow above their means.

Beware of shares

Although stock markets, particularly in the United States, are posting "record-highs" on an almost-daily basis, the report did not go so far as to call it a bubble.

"Equities might be at record highs, with sentiment overextended on nearly all fronts, but this does not necessarily point to a bubble," said Peter Garnry, the bank's head of equity strategy.

"There are some indications of a price bubble in equities, but nothing like the periods leading up to the 1987 and dot-com crashes."

At most, he conceded "a correction is likely" since investor sentiment is "so overextended that investors can only be disappointed".

The extent to which global stocks have surged recently can be tracked on the MSCI World Index — which follows the combined performance of 23 share markets including Australia, the US, UK, Hong Kong, Japan and Germany.

The report noted that the MSCI index has risen for 15 consecutive months, and is still going.

This is a record period of straight gains, without a correction.

The previous record was the 11-month rally which ended in February 2004.

As for what he sees believes might cause this 'non-bubble' to pop, the biggest risks are "policy mistakes" from China and US central banks, and whether inflation undershoots, or overshoots.