bitcoin mixing scam
A Bitcoin (virtual currency) coin is seen in an illustration picture taken at La Maison du Bitcoin in Paris, France, June 23, 2017 (Benoit Tessier/Illustration/Reuters)

Two ATM machines selling the cryptocurrency in Singapore crashed last Friday, the Straits Times reported on Wednesday.

The machines, at Hong Lim Complex and Tiong Bahru Plaza, could not sell bitcoin for three days due to "congestion in the bitcoin network", the report said quoting Bitcoin Exchange founder Zann Kwan as saying.

As bitcoin surged past US$16,000 last week, more and more investors were flocking to open new accounts or place orders.

Coinbase, the largest US bitcoin exchange, warned of outages and slow transactions, while Bitfinex, the largest global bitcoin exchange, said on Twitter that it has been under a denial-of-service attack for several days and that it recently got worse, the report said.

At the start of the year, a bitcoin cost around US$1,000. It has now skyrocketed 1,600 percent, with its market capitalisation of US$278 billion (S$376 billion) surpassing the gross domestic product of Finland and Greece.