Google employees considered blocking Breitbart on 'moral grounds', the right-wing news outlet alleged.

Breitbart claims to have received leaked emails going back to February 2017 - one month after Donald Trump entered the White House - in which staff at the tech company voice concerns about 'hate speech' and 'fake news' on the site.

The website alleges that the emails encouraged others at the company to block Breitbart from Google's lucrative Adsense advertising platform.

Google began 'plotting the downfall of this website shortly after the 2016 election', Breitbart claimed.

In one of the alleged emails, a staff member wrote that it would be 'really difficult' to prove hate speech as writers were 'artful' at demeaning others in non-explicit ways.

Another email claimed that '818' companies had taken steps to stop their ads showing on the website and that there was a 'moral argument to be made as well as a business case'.

The claim came as Google's chief executive Sundar Pichai answered questions about bias during a congressional hearing on Monday.  

He said that enabling bias would go against Google's 'core principles'.

'I lead this company without political bias and work to ensure that our products continue to operate that way. To do otherwise would go against our core principles and our business interests,' he said.

'We are a company that provides platforms for diverse perspectives and opinions – and we have no shortage of them among our own employees.'

Facebook has faced similar accusations. CEO Mark Zuckerberg denied being biased against conservatives and Trump supporters during his appearance before Congress in August.

'There is absolutely no directive in any of the changes that we make to have a bias in anything that we do,' Zuckerberg said . 'To the contrary, our goal is to be a platform for all ideas.'