Medical staff stand on a picket line outside the Royal Victoria Hospital in Belfast on Thursday as tens of thousands of public sector works took part in strike action. AFP

Unions representing around 170,000 of the region's 225,000 public sector workers called the 24-hour strike after failing to receive pay increases despite multi-decade high inflation, following the collapse of the region's power-sharing government in early 2022.

Car drivers beeped horns in support of workers at picket lines outside schools, hospitals and bus depots, adding pressure on the Democratic Unionist Party (DUP) to end its two-year protest over post-Brexit trade rules for the region.

Workers Reuters spoke to criticised the DUP but also the British government, which has pledged to provide the funds for pay rises but only if power-sharing resumes. Public pay has risen in the rest of the United Kingdom.

"We'll keep going until we get what we deserve... We've had enough," healthcare assistant and union representative Liam Stewart said outside Belfast Mater hospital.

Stewart said the squeeze on incomes had left some higher paid colleague's struggling to pay mortgages, while lower paid staff have asked the union for help accessing food banks.

The health service asked the public to "take all sensible steps" to reduce their chances of requiring care and assume any appointments due on Thursday were cancelled.

The strike began amid ice and snow across Northern Ireland, prompting warnings that only essential road journeys should be taken due to the conditions and limited gritting. Road service staff are among those set to strike for a week.

"There are a very small number of people in the DUP who are stopping this (the pay increases) from going ahead," said science teacher Dr David Roberts, who was striking for the first time in his 28-year career.

The DUP says it will only return to government once it wins further concessions on the trade rules London agreed with the EU upon leaving the bloc.

The party said its goal to ease the barriers many unionists feel undermines their place in the United Kingdom should not prevent London from immediately increasing public sector pay.

Irish nationalists and pro-British unionist politicians are obliged to share power under the terms of the 1998 Good Friday peace accord that ended three decades of sectarian violence in Northern Ireland.

Reuters