Prime Minister Boris Johnson was booed and jeered by around 200 people who gathered at the gates of Hillsborough Castle as his cavalcade drove in.
Protesters, including campaigners for the Irish language, victims campaigners and anti-Brexit activists, were among the crowds who held aloft banners.
Mr Johnson is meeting the main Stormont parties at the royal residence in the village on Monday afternoon amid the latest impasse in power-sharing government at Stormont.
Protesters held banners which read: “Back off Boris. Protect The Protocol."
Boris Johnson arrives at Hillsborough Castle
Liam McBurney
There was also a demonstration by some of the families of the 11 people killed by soldiers in Ballymurphy in west Belfast in 1971 against plans by Government to offer an effective amnesty to prosecution for Troubles offences.
Protesters held aloft banners
Liam McBurney
It comes after an Irish minister said a UK Government move to unilaterally override the Northern Ireland Protocol could endanger the wider Brexit trade deal.
Foreign Affairs Minister Simon Coveney urged Boris Johnson to commit to further engagement with the EU to resolve the Irish Sea trading dispute, rather than breaking international law by acting alone.
Tensions between London and Brussels are intensifying over the prospect of Mr Johnson using domestic legislation at Westminster to nullify parts of the Brexit Withdrawal Agreement that require checks on goods moving between Great Britain and Northern Ireland.
Foreign Secretary Liz Truss is expected to formally announce a plan to legislate on the Protocol on Tuesday, although an actual parliamentary Bill is not expected to be published at that point.
Mr Coveney’s comments came ahead of Mr Johnson’s visit to Northern Ireland on Monday for emergency talks with Stormont’s political leaders in a bid to break a deadlock caused by the Protocol.
The power-sharing institutions in Belfast have been plunged into crisis in the wake of the recent Assembly election, with the DUP refusing to re-enter a devolved government in protest at trading arrangements the party claims are undermining the union.
The EU has made clear that unilateral action from the UK to walk away from the Protocol deal would represent a clear breach of international law.
Dozens waited for Mr Johnson's arrival
Liam McBurney
Mr Coveney, who was in Brussels on Monday, warned that the entire UK-EU Trade and Co-operation Agreement deal – the TCA – could be jeopardised if Mr Johnson takes unilateral action on the Protocol.
He said: “This is a time for calmness, it’s a time for dialogue, it’s a time for compromise and partnership between the EU and the UK to solve these outstanding issues.
“If that is the approach taken by the British Government then we can make significant progress and we can make progress quickly to respond to the concerns of both the business community and the unionist community in Northern Ireland.
“That alternative is unilateral action which means tension, rancour, stand-offs, legal challenges and of course calls into question the functioning of the TCA itself, because the TCA and the Withdrawal Agreement are interlinked, they rely on each other.
“That is the last thing Europe needs right now, when we are working so well together in the face of Russian aggression and responding to the support needed for Ukraine at this time.”
Prior to his visit to Northern Ireland, where he will hold talks with the five main parties at Hillsborough Castle, Mr Johnson insisted he did not favour scrapping the Protocol, rather amending it to reduce disruption on Irish Sea trade.
Northern Ireland’s 1998 Good Friday/Belfast peace agreement contains provisions to protect and develop relations both on a north/south basis on the island of Ireland and on an east/west basis between the island and Great Britain.
Mr Johnson claims the Protocol has upset this “delicate balance” of unionist and nationalist aspirations by undermining the east/west dynamic.
On Monday, a Foreign Office source told PA Media that Ms Truss’s priority was about upholding the Good Friday/Belfast agreement and restoring stability.
“We’re not after a fight with the EU,” the source insisted.