A cyber attack which started in Ukraine is now affecting countries across the world

A huge cyber attack that initially hit Ukraine appears to be spreading across the world.

The hack was already the biggest in Ukraine's history when it hit that country. But it appears to be making its way to other countries – including Spain and India – and may be functioning like the massive "Wannacry" attack, according to cyber security experts.

The attack is hitting major infrastructure in the countries where it has spread to. That has included companies ranging as widely as Danish shipping company Maersk and British advertising company WPP.

The British National Cyber Security Centre said that it was "aware of the global ransomware incident" and is "monitoring the situation closely".

Maersk said that it didn't yet know the cause of the outage but that it suspected it could extend across all of its global operations.

Some security experts have even suggested the attack could be bigger than the Wannacry attack, which spread across the world in May. That was most famous for hitting the NHS and locking down computers across hospitals and doctors surgeries, but it also hit other major companies internationally.

At the time, cyber security professionals warned that a repeat attack could be launched that would be even bigger than that crippling hack.

Initial reports had suggested the hack was a co-ordinated hack being launched at Ukraine and Russia at the same time. It's not clear how it began, or how it made its way to other countries.

Cyber security experts also don't yet know whether it's possible to mitigate against the attack, or how it gets into computers.

Russia's top oil producer Rosneft said a large-scale cyber attack hit its servers on Tuesday and computer systems at some banks and the main airport in neighbouring Ukraine were also disrupted.

Britain's WPP, the world's biggest advertising agency, said on Tuesday it had been hit by a cyber attack, one of many major corporations to face major disruption.

A spokesman confirmed it had been affected without giving any further details. The company's website was not available.

Seventeen shipping container terminals run by APM Terminals have been hacked, including two in Rotterdam and 15 in other parts of the world, Dutch broadcaster RTV Rijnmond reported on Wednesday.

APM Terminals is a subsidiary of shipping giant Maersk , which has confirmed it is suffering from a cyber attack.

APM's website was difficult to reach and phones at its headquarters in The Hague and offices in Rotterdam went unanswered.

A spokeswoman for the company in Copenhagen confirmed its systems were "impacted" as part of Maersk's IT infrastructure.

The RTV report said computers were infected by ransomware that encrypted their hard drives. The broadcaster published an image of the screen of an affected machine with a message demanding a $300 payment.