LONDON (Reuters) - Twitter users are talking about Britain leaving the EU around twice as much as they are discussing staying in, data showed on Wednesday, as some observers look to social media to help track the likelihood of a Brexit.

With polls too close to call, hashtags related to a "Leave" vote have received over 800,000 mentions, against more than 400,000 for "Remain," according to an analysis by social media monitoring tool Brandwatch.

Up until June 7, there were 5.4 million tweets mentioning the EU referendum in the last two months, it said.

"Of course, this doesn’t necessarily mean that more people using social media will actually vote Leave and these mentions will include people who are talking about the Leave campaign but don’t necessarily support it," it added on its website.

"However, the fact that Leave-related hashtags are registering at nearly double the rate Remain ones are is definitely interesting."

Pollsters have so far struggled to call a clear outcome for the June 23 vote. On Monday, two online surveys had the Leave camp as in the lead but only hours later two other polls showed Britons narrowly favoring the Remain option.

BlackRock, the world's biggest asset manager, said on Tuesday it was now using Twitter to track activity in both camps in a quest for clarity.

The economy and immigration have so far dominated conversation, the Brandwatch data showed. Prime Minister David Cameron is the most mentioned political leader, followed by "Vote Leave" figurehead Boris Johnson and eurosceptic UKIP leader Nigel Farage.

(Reporting by Freya Berry; editing by Stephen Addison)