Fears of Christmas chaos in frontline services have grown after buses and trains were hit by a surge in Covid-related absences.

Luas, rail and bus services were disrupted yesterday due to low staffing levels caused by the virus.

The disruption came as a letter to the HSE warned that staff are suffering from “burnout” and have been asked to forfeit annual leave.

In a customer notice, Transport for Ireland said some public transport services were not running to schedule due to a “high level of Covid-related staff absences”.

Iarnród Éireann said the M3 Parkway to Docklands service would operate between M3 Parkway and Clonsilla only.

Customers were advised to transfer to Maynooth-to-Dublin services at Clonsilla.

“This is due to staff availability, arising from current Covid-19 levels and close contact public health compliance,” it tweeted.

A National Transport Authority spokesperson said some operators experienced localised increases in absence levels “which leads to a limited number of services being cancelled at short notice”.

The spokesperson said 2pc of absences are Covid-19-related, and at present there is no immediate cause for concern on most services.

As Omicron spreads, representative bodies and unions for frontline workers spoke of their concerns about the impact of the new variant on staffing levels.

A letter from the Staff Panel of Health Sector Trade Unions to the HSE warns that a significant number of members had outlined that their leave is to be postponed.

It called for higher-grade respiratory masks to be used as standard, and Hepa filtration systems to be installed in every patient or worker area as the variant becomes more prevalent.

“It is incumbent on me to highlight to the HSE that their staff, our members, are exhausted and suffering from burnout,” said the letter from chair Tony Fitzpatrick.

“This workforce that has given total commitment to its employer over the last 18 months. It appears that the HSE have no regard or respect for health service staff that are already on their knees.”

Mr Fitzpatrick told the Irish Independent it is inevitable that there will be more cases among healthcare workers, although they have a less restrictive close contact system.

“There is a concern that Omicron is more transmissible and potentially more staff will be out. Services are under massive pressure,” he said.

A Garda Representative Association spokesperson said the available number of frontline gardaí is falling across the country.

He said new rules in November meant the percentage of gardaí that could take annual leave at once had been cut to deal with any potential new Covid measures.

“We are being told of shortages across the organisation but particularly on regular frontline units who provide the immediate response to calls from the public,” he said.

“Less gardaí means a reduction in the service that can be provided and can pose a danger to both our members and the communities they serve.”

A senior Garda source said workforce numbers have not fallen dramatically due to infection rates but there are fears that that could change if Omicron becomes dominant.

The number of enhanced illness benefit claimants has more than doubled from just over 2,000 in August to over 4,500 this month.