The developer of a proposed data centre in Cardiff has said it is also seeking permission to build a gas power plant to get it up and running.

Developer Curtis Hall said the plant, which could operate for up to five years, may be needed if the site cannot get on the national grid quick enough.

It also said the gas turbine plan was a "worst-case scenario", and the project - planned for the site of an existing park and ride near Llanrumney - would bring significant benefits.

Friends of the Earth called it "climate-wrecking" infrastructure, and almost all the area's Members of the Senedd (MSs), and a Welsh government minister, have now formally objected to the plans to build the data centre.

A senior Labour councillor from Cardiff council - which has an agreement to sell the site to the developer - had also objected.

The Welsh government is considering whether it will take over the planning process for the facility - meaning Cardiff Council is unable to grant planning permission in the meantime. The government is also planning to publish its own policy on the wider issue by the end of the year.

Interest in building data centres has increased with the rise of artificial intelligence (AI) technologies - but they have been controversial worldwide, in part for the amount of electricity they require.

Cardiff East Park and Ride currently serves staff and patients using Cardiff's University Hospital of Wales.

Some of those living in a new-build housing estate nearby are concerned about the project, including James George, 32, who said he was worried about the impact on the environment and his home.

"The main concern is the noise and the pollution, like they have to run a diesel generator in case of any power disruption," he said.

Alexander Grant, 51, said: "My main worry is the situation with the Heath hospital with regards to the staff and the patients." "There's also other reasons as well, from the environmental side of things.

I think it's an absolute travesty."

Dale Harvey said he was concerned it would add the noise from the A48 dual carriageway, saying the proposal was "not great".

"You buy a new build, and we're being told all of a sudden there's going to be generators run - all the fumes and all the noises," he said.

The developer said the site would not be audible locally, and air quality would not have a significant impact.

Planning documents for an outline planning application detail a "temporary ancillary energy centre" with gas turbines that have a maximum generating capacity of 49.9MW.

They say that the energy centre is "proposed to start in operation in July 2028 and last approximately for five years until the site has a full electricity connection [until July 2033]".

The centre, according to the documents, would include five gas turbines, a steam generator, and another two gas turbines on standby. In the long-term the data centre would require a connection of 150MW from the national grid.

This may not be delivered, however, until between 2030 and 2034. Energy generation facilities of 50MW need planning permission from the Welsh government.

Curtis Hall denied it was trying to avoid having to make such an application by limiting the plant to 49.9MW.

Another 40 diesel backup generators would also be needed after a connection is made to the grid to ensure "continuous power".

The use of fossil fuels to power the centre prompted criticism from environmental campaign group Friends of the Earth Cymru.

Its interim director Jenny Lloyd said: "After a summer of heat waves and drought and worries about flooding over the autumn and winter, it's completely irresponsible to give the green light to this climate-wrecking piece of infrastructure." Plaid Cymru MS Nick Carter, who represents Cardiff's Caerdydd Fynnon Taf constituency, said: "There is no reason why a data centre needs to be sited in an urban area close to schools and care homes, when in fact underneath the headlines is a small gas-fired power station."

Senior Labour councillor Lee Bridgeman added his voice to those objecting this week.

The member of the Cardiff Council cabinet and Llanrumney ward councillor said in a letter it was "hard to reconcile" the centre's emissions "with Cardiff's climate emergency declaration and Planning Policy Wales".

As well as the data centre, the plans included a new bridge and link road for pedestrians and cyclists. Curtis Hall previously had planning permission for a logistics centre.

According to Cardiff Council the company had switched to a data centre because of "changing market demand". The company said the gas generation was "not the data centre's permanent power supply, and once the grid connection is live it would no longer be needed".

"If the connection arrives in time, the energy centre will not be needed at all," it said. "Gas turbines appear in the planning documents because they represent the worst case for emissions and noise, so assessing them tests the upper limit of any impact." The company said the technology was "not confirmed" for the energy centre - suggesting fuel cells that convert gas or hydrogen to electricity could be used.

It said the air quality effects of gas and diesel generators were also "not significant".

In response to climate change concerns, Curtis Hall said south Wales' electricity grid was "decarbonising fast" with plans for floating offshore wind.

A spokesperson for the company said the development would bring "significant benefits", such as "the delivery of the new road bridge" and by helping "attract much-needed investment, create well-paid jobs and provide new training opportunities". According to Cardiff Council's website, formal objections have been made by all of Caerdydd Ffynnon Taf's Plaid MSs, including Constitution Minister Dafydd Trystan Davies, Labour MP Alex Barros-Curtis, Green MS Paul Rock, and Labour MS Shavanah Taj.

Reform's Cai Parry-Jones had also raised concerns.

Requests were made by Plaid MSs Nick Carter and Zaynub Akbar for the plans to be called-in by Welsh government, as had local Cardiff Liberal Democrats.

The two Plaid MSs say the issue "should be a question of national policy, not determined piecemeal" by individual local councils "without guidance".

A spokesperson for Cardiff Council said the planning application was still being considered and would be reported to a formal planning meeting in future.

It said the Welsh government's holding direction - which prevents a decision being made while ministers decide whether to take on the planning application - was "not unusual, given the significant level of public interest in the application". Cardiff Council has said it was looking at for an alternative site for the park and ride.

A council consultation is running until 28 October. The Welsh government is separately drawing up its own "sustainable development policy" on data centres generally - planning minister Siân Gwenllian promised Plaid Cymru conference that it would be published before the end of the year.

At Plaid Cymru's conference in Llandudno earlier in October, Gwenllian told party members: "These data centres are needed to sustain a modern economy." But while she said they must benefit the economy, she said the facilities "must be on our terms".