Closing down M4 junctions around Newport would be “catastrophic” and “shift the problem” of motorway traffic onto the city’s roads, councillors have warned.

There was nearly unanimous support for “proactive” opposition to any junction closures as the new Welsh Government reconsiders ways to fix M4 congestion.

To date, the government has not said explicitly it would support or pursue junction closures, but Newport councillors have made their stance clear ahead of any future announcements on alternatives to a relief road.

Cllr Dimitri Batrouni, the council leader, said traffic in Newport was “already bad at peak times” and was made worse by “any logjam on the M4”.

Closing junctions would cause “mayhem”, he told a council meeting, and claimed “penalising Newport residents and businesses for an M4 traffic problem is not acceptable”.

His motion was backed by other Labour members, including Cllr Pat Drewett, who said “easy access to the motorway network is one of Newport’s greatest economic strengths”.

The council’s Conservatives agreed, but pointed out the relief road had been scrapped by a Labour First Minister, Mark Drakeford.

Cllr Matthew Evans said his Tory group had long opposed shutting M4 junctions, and was willing to join an “unholy alliance” in the council chamber to reject closures he claimed would have “a catastrophic effect” on the city.

Labour councillor Deb Davies, the authority’s deputy leader, said in Newport her party’s stance was “unchanged” since the relief road was proposed, and had wholly backed the project.

Cllr Davies warned Newport’s roads are “already under pressure”, and junction closures could make city traffic “even worse”.

The council’s motion “sends a clear message” to the government that “we welcome the investment in public transport [and] … we support measures that genuinely improve congestion and connectivity”.

“We cannot support proposals that shift the problem from the motorway onto streets where our residents live, work and raise our families,” she added.

Cllr Lauren James said the Greens were also opposed to junction closures and “don’t want to see M4 traffic diverted through Newport”.

But councillors rejected her calls to continue backing the so-called Burns programme delivering a ‘network of alternatives’ to a relief road.

Labour and Tory members told her they had concerns about some Burns ideas around road tolls and changes to Old Green Roundabout.

Except for its opposition to tolls, the Labour-led council has until now been broadly supportive of the Burns programme, with a seat at the table on the regional transport commission.

Cllr James said continuing to back Burns’ overall aims did not mean the council had to accept less popular recommendations, such as tolls.

“I’m sure we’ve all heard enough from our constituents that they want solutions now,” she said. “They don’t want to wait another 30-40 years.”

Wales’ deputy transport minister said in June the government would consider “all other road options” than a relief road when looking at how to tackle M4 issues around Newport, and will report back in the autumn.

Cllr Miqdad Al-Nuaimi, an independent, told the council meeting he was “not aware that currently there are any hard proposals from the Welsh Government for closing junctions on the M4”.

But Cllr Mark Howells, from the Lliswerry independents, said the motion was “proactive”.

“We’ve got a real opportunity to shape what we think Newport should look like, not wait to be consulted by the Welsh Government about what they want to do,” he said.