Firefighters reported a “significant decrease” in emergency calls linked to Loyalist bonfires in Northern Ireland, as annual Battle of the Boyne commemorations got under way.

The Northern Ireland Fire & Rescue Service (NIFRS) responded to 34 bonfire-related incidents on Thursday night, when hundreds of fires were lit on the first night of the celebrations marking the anniversary of William of Orange’s victory in 1690.

The fire service said this was down from last year and the lowest number of callouts since 2015.

The majority of incidents required “limited intervention” by one fire appliance.

Its statement added: “There were no attacks on NIFRS crews or appliances whilst carrying out their operational activities throughout the province.”

Police officers came under attack from petrol bombs at a community interface area in north Belfast, and two youths were arrested in the Nationalist Springfield Road.

A 16-year-old boy was arrested on suspicion of unlawful assembly and a 17-year-old boy was arrested on suspicion of riotous behaviour. Both were released on bail pending further inquiries.

A man, 52, has also been charged in relation to the placement of offensive items, namely election material, on a bonfire in Lisburn. This year’s celebrations come at a time of changing demographics and continuing constitutional crisis in the province.

Population data indicates that Catholics will soon outnumber Protestants, while the combination of a political vacuum at Stormont and the questions raised by Brexit has prompted speculation about the region’s future direction.

Earlier this week, MPs voted in support of passing legislation that would introduce same-sex marriage and extend abortion rights in Northern Ireland unless devolved rule is resumed by October.

Northern Ireland’s power-sharing arrangement collapsed in January 2017 amid a bitter split between governing parties the DUP and Sinn Fein, leaving the province without normal day-to-day government.

A majority of the population in Northern Ireland had also voted Remain in the EU referendum, making the fallout of the Brexit negotiations – and its potential to destabilise the Good Friday Agreement – a particularly bitter blow for people living there.

There has even been serious speculation that a border poll, asking citizens if they would prefer to leave the UK and join a united Ireland instead, could take place within a decade.

Some so-called “soft” Unionists have also expressed openness to quitting the UK if Brexit unravels the economy.

Amid this climate, the tradition of lighting bonfires is seen as an important opportunity for the Loyalist community to celebrate its history.

Hundreds of bonfires were lit on Thursday night – the eve of the “Twelfth” – and burned into yesterday morning to mark 329 years since King William defeated Catholic King James II and paved the way for the rise of Protestantism as the dominant faith.

A key flashpoint in this year’s commemorations, however, had been the controversial bonfire at Avoniel leisure centre.

The local council, where Sinn Fein is the biggest party, had tried to ban it on health and safety grounds, prompting a graffiti warning to the contractors tasked with removing the pyre that they “attack Loyalism at your own risk”. The company involved subsequently pulled out.

The council has asked police to investigate how the contractor’s identity came to be leaked but backed out of banning the bonfire.

It was lit on Thursday amid claims Loyalists had “won a hugely symbolic victory”.

Police Service of Northern Ireland Assistant Chief Constable Barbara Gray said yesterday she was relieved “we haven’t seen a repeat of the violence we witnessed on our streets this time last year”. However, she said she believed the paramilitary Ulster Volunteer Force (UVF) had played a role in inflaming tensions. She said: “I have no doubt that at Avoniel there was influence from East Belfast UVF, I have absolutely no doubt about that.”