The National Security Agency (NSA) has pulled the plug on its controversial mass phone data collection system in accordance with the terms of the USA Freedom Act, according to Digital Spy.

Although the Senate Bill restricting the agency's surveillance powers has been law for six months, the NSA was given until 11:59pm ET on November 28 to switch to a new programme.

The group no longer has unrestricted access to phone metadata from operators including Verizon and AT&T, and must now obtain court orders on a case-by-case basis to view records.

The Freedom Act also requires the NSA to offer transparency about the data it has requested in the form of annual reports.

The House of Representatives passed the USA Freedom Act in May, despite fierce Republican opposition led by Senate Majority Leader Mitch McConnell.

It was drawn up following the 2013 revelations from whistleblower Edward Snowden, who exposed the NSA's data-collecting practices before fleeing the country.