Former US Secretary of State Hillary Clinton is expected to make an official announcement of her 2016 presidential campaign on Sunday, media reported.

According to an official, she is likely to make the announcement via video footage and social media as she kicks off her long-expected second shot at the presidential run-off, New York Daily News reported.

Clinton is expected to begin her campaign with a series of smaller events in early-voting states, including Iowa and New Hampshire, the official said.

After her defeat to incumbent President Barack Obama in 2008, Clinton had firmly said "no" when asked whether she would run for the presidency again.

However, her position has evolved in the past few years.

The Clinton camp has already signed a lease for a new office space in Brooklyn, New York, as her campaign headquarters.

Hillary Clinton served as the 67th Secretary of State under Obama from 2009-13. Prior to this, she represented New York in the US Senate from 2001-09.