London (CNN) At the stroke of midnight on Monday, Northern Ireland's restrictive abortion and same-sex marriage laws came to an end, after the region failed to restore its power-sharing executive that collapsed more than 1,000 days ago.

The changes were imposed by lawmakers in Westminster, who had given Northern Ireland a deadline until October 21 to restore its assembly at Stormont or have the laws changed directly from London.

Despite the Stormont assembly meeting on Monday morning for the first time in three years, it was unable to prevent the amendments that meant same-sex marriage would be legalized and abortion would be decriminalized in the province.

Abortion-rights demonstrators march through the streets of Belfast ahead of a meeting of the Stormont Assembly.

Campaigners on both sides of the debate gathered outside Northern Ireland's parliament building in Stormont on Monday, ahead of momentous reforms to some of the most restrictive abortion laws in the world.

Many campaigners posted videos on social media of the countdown to midnight.

One of them, 24-year-old Alisha Rooney told CNN: "I am thrilled that finally my friends and colleagues can marry without it being a crime in this country.

"I am thrilled that women now have the choice with what they can do with their own bodies."

Words cannot describe this euphoria felt across Northern Ireland tonight 🏳️‍🌈💜 FINALLY we are moving into the 21st century and celebrating that LOVE IS LOVE no matter your gender or sexual orientation 🌈💜 #LoveIsLove #EqualMarriage #northisnow pic.twitter.com/kewxrb5kMG — 🎃 𝕿𝖍𝖊 𝕯𝖊𝖗𝖕𝖋𝖆𝖈𝖊 𝕲𝖎𝖗𝖑 🎃 (@BANGWOOL_PD) October 21, 2019

Another campaigner, 20-year-old Jamie Kennedy, told CNN, "we tend to have a bad reputation for being 'stuck in the dark ages' when it comes to equality and rights but we've now shown we value our LGBTQ community as equals and we value the choices that (often in tragic circumstances) pregnant people have to make regarding their reproductive health. I've never felt prouder to say I'm Northern Irish."

Ok I actually posted the wrong video lol here's the countdown to midnight ✊🏳️‍🌈 pic.twitter.com/5Yg9bDj631 — Jamie 🎃 (@JkUmisma) October 22, 2019

People gathered at the Maverick bar in Belfast to celebrate and the atmosphere was joyful, according to locals.

"There were people who didn't know each other but were talking to each other, hugging each other, singing together and dancing together. There was a countdown to midnight when the laws came in and the eruption of cheer and applause was bigger than any New Year's party I've been to," Ciaran Gallagher, 30, told CNN.

Less pleased was Northern Ireland's Democratic Union Party leader, Arlene Foster, who after the leaving the chamber said, "it is a very sad day," according to Reuters.

"I know some people will seek to celebrate and I would say to those people, think of us who are sad today and who believe this is an affront to human dignity."

Westminster steps in

The UK Parliament voted earlier this year for measures designed to keep the region running in the absence of a devolved government.

It set out that if the power-sharing executive was not restored by October 21, Westminster would introduce regulations that would make same-sex marriage and abortion lawful from January 13, 2020 and March 31, 2020.

While access to abortion services won't be fully in place until March, the legislation stipulates that from October 22 women will no longer be prosecuted for seeking abortion services.

Abortion rights supporters pose outside Stormont in Belfast on Monday.

Monday marks almost three years since Northern Ireland 's joint government, made up of nationalist and unionist lawmakers, collapsed after Deputy First Minister Martin McGuinness -- who died in 2017 -- stepped down because of a spat over a renewable energy policy.

Northern Ireland's complex power-sharing arrangement -- established as part of the peace process -- means that both the nationalist Sinn Féin party and the Democratic Unionist Party (DUP) must work together, and appoint a First Minister and Deputy First Minister who would lead the executive together.

A snap election after McGuinness stepped down led to Sinn Féin, which wants a united Ireland, winning 27 seats -- one fewer than the DUP, the largest in the Executive.

Since then, both parties have failed to reach an agreement -- with each blaming the other for it -- and the region has been governed without ministers, with its civil service operating its day-to-day administration, except without the ability to make key policy decisions.

Abortion rules contravene UK human rights laws

Despite abortion being legalized in the UK when the 1967 Abortion Act was passed, it has never been extended to Northern Ireland -- where a law from 1861 still exists.

The legislative actions by Westminster bring Northern Ireland's laws into line with the rest of the UK. The region has one of the most restrictive abortion laws in the world, with the procedure carrying maximum sentences of life imprisonment, even in cases of rape, incest and fatal fetal abnormality.

For years, MPs across the political divide urged the UK government to change the law in Northern Ireland; the region's laws came under increased scrutiny after the Republic of Ireland legalized abortion following a referendum in 2018.

Women in the province have been forced to travel to other parts of the UK to access terminations, and earlier this month the High Court in Belfast ruled that its abortion rules contravene UK human rights laws.

The case was heard by Justice Keegan after Sarah Ewart challenged the law having been denied an abortion in Northern Ireland in 2013, even though doctors had said her unborn child would not survive outside the womb. Instead she traveled to London to end her pregnancy.

The judge said the prospect that another woman would have to face the same "trauma and pain" should be avoided in future.