Rare features and printing errors on some Australian coins that are still in public circulation could make prospective coin collectors a small fortune.

There are currently five coins across 20 cent, one dollar and fifty cent denominations that could be worth thousands of dollars.

Typo spotted in $50 note, in the video below.

2000 ‘mule’ one dollar coin

Earlier this year, a Melbourne mum revealed how a simple mistake on a batch of one dollar coins could earn you $3000.

A mix up at a mint in 2000 created a rare $1/10c hybrid - also called a mule coin - which is valued by rare coin collectors at thousands of times its face value.

The coin was made when a technician at the Royal Australian Mint accidentally paired the kangaroo-patterned ‘tails’ side of the coin with the ‘head’ of a 10c piece, explains the Australian Coin Collecting Blog.

The majority of the coins wound up in Perth, and while the mule frenzy peaked around 2003/2004, the rare coin is still in circulation.

It’s a timely reminder to check your one dollar coins from now on, as you might just win a jackpot.

Find out more in the video below.

2007 ‘double head’ five cent coin

Sometimes the coins that you might not think are worth much are actually worth the most.

The Australian Coin Collecting Blog explains that the ‘double head’ was deliberately paired by a Mint worker using two 2007 head dies. The press was then run, and it’s estimated thousands of coins were printed.

If you come across one, you could earn yourself a massive 299900 per cent return on the face value of the coin.

You can read up more on this coin here and tips on how you can spot it.

2010 ‘upset’ 50 cent coin

An operator error during a 2010 production run of Australian 50 cent coins where the die was installed incorrectly caused the heads of some coins to be rotated at 30 degrees from the reverse ‘tails’ side of the coin.

There were an estimated 200,000 of these coins in circulation.

It might be a very hard to spot the error, but some of these coins have previously sold for $50 on eBay.

You can read more on The Australian Coin Collecting blog here.

2000 ‘incuse flag’ 50 cent coin

The 50 cent ‘millennium’ coin is one of the hardest errors to spot and is also known as the ‘incuse flag millennium’ coin.

The mistake affects the Cross of St. Andrew on the Union Jack which is sunk into the coin rather than raised in the widely circulated version.

It’s believed that there are only around 200,000 of these coins in public with a value of around $50.

1966 wavy baseline 20 cent coin

On most Australian 20 cent coins, the base of the number two is a straight line. But in a series of coins released in 1966, the base has a slight curve in the shape of a wave.

Though it’s a minor detail, it can multiply its value to collectors hundred-fold.

One of the coins is selling on eBay for $300, with members in a coin collecting Facebook group saying the same coin could go for up to $800.

The Royal Australian Mint, which manufactures Australia’s coins, says it tries to limit mistakes or misprints and understands why “error coins” become circulated.

However, even with the strict screening process, it’s impossible to say exactly how many have made their way into Aussie wallets.

“Due to the rarity of these coins, avid coin collectors are continually on the hunt in effort to add these valuable coins to their collections,” a spokeswoman for the Mint previously told 7NEWS.com.au.