A woman was killed and up to six others injured in a mass stabbing in Russell Square in the center of London at around 10:30 pm, Wednesday, Metropolitan Police have confirmed.

A man has been arrested and police say a taser was used by one of the arresting officers.

"Terrorism is one possibility being explored at this stage," a police statement said.

London had already announced that it would increase its presence of armed police following the recent terror attacks across Europe, authorities said.

As part of a new anti-terrorism operation, 600 additional armed officers will be present in highly visible locations across the UK capital to protect against the threat of attacks.

In a statement, Metropolitan Police Commissioner Bernard Hogan-Howe said: "Anyone who's been following events in Europe over the past few weeks will understand why we want to show our determination to protect the public."

While the threat level has not changed and remains at "severe", authorities said it's important they're prepared following recent attacks in France, Belgium and Germany.

London Mayor Sadiq Khan said that while additional armed police will be on the streets, there is no reason to be alarmed.

"It is important we are prepared should the unthinkable happen," Khan said.

While the operation is not based on any specific intelligence, Hogan-Howe said earlier this week that the risk of a terror attack in the UK is a case of "when, not if".

He said on the police's official blog Sunday he believes the threat of terrorism is real and expresses "a greater sense of fear that Britain will be the next victim".

Britain's senior counterterrorism officer, Mark Rowley, also has admitted police were preparing for "enormous and spectacular" attacks on the UK. A police press officer later said Rowley's comments did not refer to a specific known plot but a general threat.

Meanwhile, a new report from Britain's Home Affairs Committee said its Border Force has a "worrying low" number of boats patrolling the UK coastline.

It said only three boats were available to patrol more than 7,500 miles of coastline, compared with some other European countries that have at least 100 vessels for much smaller coastlines.

The Border Force "has been given a key role in implementing strengthened coast security measures," the report said. But it is under-resourced due to "problems in gaining access to a sufficient number of patrol boats".

The committee said rigorous steps needed to take place, as smaller ports are being used by criminal gangs to move people between Europe and the UK.

The force said it needed to be given all the necessary equipment, including vessels, to allow it to carry out its responsibilities effectively.