US President-elect Donald Trump has appointed his son-in-law Jared Kushner as his senior White House advisor, in a move that could test anti-nepotism laws.

"Jared has been a tremendous asset and trusted advisor throughout the campaign and transition and I am proud to have him in a key leadership role in my administration," Mr Trump in a statement.

Mr Kushner, 35, was a hugely influential if largely discreet confidant to his father-in-law during his 2016 campaign for the White House, but there are legal questions that could complicate his potential new job.

"Mr Kushner is committed to complying with federal ethics laws and we have been consulting with the Office of Government Ethics regarding the steps he would take," NBC News quoted Mr Kushner's lawyer as saying in a statement.

Like Mr Trump, Mr Kusher is a property developer. (AAP)

Mr Kushner, a property developer and magazine publisher who has been credited with being the brains behind the scenes that helped get his father-in-law elected, is married to Mr Trump's eldest daughter Ivanka.

A federal nepotism law, passed after then-president John F. Kennedy appointed his brother attorney general, prohibits any president from hiring a relative.

But Mr Trump's advisors have previously said there might be more leeway when it comes to the White House, rather than the cabinet.

Meanwhile, Mr Trump has again stirred controversy after he lashed out on Twitter at actor Meryl Streep.

Streep used an award acceptance speech at the Golden Globe awards to criticise the president-elect's mocking of a disabled reporter on the campaign trail.

Mr Trump hit back on his favourite online medium, labelling the esteemed actor "over-rated" and a "Hillary [Clinton] flunky".

Read more: Trump fires back at Streep after Golden Globes speech