Chinese personal computer maker Lenovo has signed a non-disclosure deal to examine the books of troubled Canadian smartphone maker BlackBerry Ltd, the Wall Street Journal said on Thursday, quoting unnamed sources.

Smartphone pioneer BlackBerry said in August it was exploring strategic options that could include an outright sale.

It has received a tentative $9 a share offer from a consortium led by its largest investor, Prem Watsa's Fairfax Financial Holdings Ltd, which wants to buy BlackBerry for $4.7 billion and take it private, and other companies are also taking a look at the company's books to decide whether to make an offer, industry sources say.

A Chinese bid for BlackBerry would likely face opposition from the Canadian government, which vets foreign takeovers to ensure they are in the national interest, and that they do not threaten national security.

BlackBerry products have struggled to compete against the Apple Inc iPhone and the numerous devices powered by Google Inc's Android operating system.

A new line of smartphones that run on the BlackBerry 10 operating system has also failed to re-ignite sales, prompting the company last month to announce that it would slash its global workforce by more than a third.