Hundreds of protesters gathered outside Parliament as MPs began debating Donald Trump's state visit to Britain.

In a packed Westminster Hall, MPs were considering Theresa May's decision to extend the invitation to the US president in a debate being held in response to petitions signed by millions of Britons.

Anti-Trump chants were heard from Parliament Square before the debate, and appeared to die down as Newport West MP Paul Flynn opened proceedings.

MPs were debating a petition signed by more than 1.85 million people, calling for the visit to be stripped of the trappings of a state occasion in order to avoid causing "embarrassment" to the Queen.

They were also considering an alternative petition, backed by almost 312,000 signatories, demanding the state visit goes ahead.

Opening the discussion, Mr Flynn highlighted the fact that Mr Trump is only the third US president to be given the honour of a state visit and said he was invited too soon in his already highly controversial presidency.

Barack Obama only received an invitation after 758 days, while it took 978 days before his predecessor, George W Bush, was offered a state visit, compared with seven days for Mr Trump.

Mr Flynn repeated comments made by former Foreign Office permanent secretary Lord Ricketts, who said the Queen has now been put in a "very difficult position".

The Labour MP added: "I believe for that reason alone that we should consider this, and the Government should consider this with a bit of humility... and change the invitation to one for a visit, not a state visit."

In its official response to the petitions, the Government stressed ministers believe "the President of the United States should be extended the full courtesy of a State Visit".

"We look forward to welcoming President Trump once dates and arrangements are finalised," the response said.

The Stop Trump coalition has called a nationwide day of action and dozens of protests have been co-ordinated by the One Day Without Us movement celebrating the contribution of immigrants to British society.

The rally in Parliament Square, which organisers claimed will attract more than 20,000 people, will be addressed by speakers including joint Green Party leader Caroline Lucas and comic Shappi Khorsandi.

Celebrities backing the action include singer Paloma Faith, who said: "I'm backing the protests because I believe in human rights and compassion and Trump evidently does not."

Calls for the state visit to be cancelled have been backed by London mayor Sadiq Khan, who hit out at the president's "cruel and shameful" policies.

Mr Khan said the controversial tycoon's travel ban aimed at people from seven Muslim-majority countries, which has run into trouble in the US courts, and the suspension of refugee admissions were reasons not to be "rolling out the red carpet".

Commons Speaker John Bercow has also become embroiled in the row after effectively banning Mr Trump from addressing MPs and peers during his visit.

A motion of no confidence in the Speaker was tabled as MPs left for the February recess, but with Parliament returning on Monday both Mr Bercow's critics and supporters will be seeking allies.