Metro mayor Dan Norris has struck a cautious note over the prospect of a Bristol underground.

The new head of the West of England Combined Authority (Weca) says he cannot rule it in or out because of the project's estimated £4billion costs, and plans to focus on developing bus services in the nearer term.

Fellow Labour mayor of Bristol Mr Rees has long talked up the city getting a London-style tube network as part of a mass transit system of fast, reliable public transport services.

It was also a pledge in his 2021 election manifesto which said mass transit would be "in the form of an underground and overground", alongside improving and expanding existing infrastructure.

Mr Norris appears unsure over the idea, which opposition Conservative councillors have branded "pie in the sky", and says his "instinct is that undergrounds cost a lot of money".

Asked by BBC Radio Bristol's John Darvall on Thursday (May 20) whether it would actually go ahead, the West of England mayor said: "It's theoretically possible but I need to see all the plans.

"I understand the Department for Transport (DfT) has been looking at all the various options and we need to have a discussion.

"I will be a key player in that and I will do whatever needs to be done to get us the good public transport system we've never had and that we deserve and need.

"Whether that is an underground or not, I really don't know because my instinct is that undergrounds cost a lot of money because it's digging and money will be hard to get hold of.

"But I don't rule it out at this stage, it would be foolish to do that.

"It might have some merit but I have to say I don't rule it in either automatically.

"I will be looking at it and weighing it all up."

Mr Norris said a mass transit system for the city and region would not be up and running for at least another decade.

He said: "In the short term it will require better buses.

"Anything that gets built will take 10 to 12 years, so I don't think people are happy to put up with the system as it is now for that long.

"So in the medium and short term we will need to do things with buses and in the longer term consider exciting things like trams and other forms of major public mass transport.

"Rural buses need to be a big part of this because the West of England mayor doesn't just represent the cities but the rural communities too."

Mr Norris said he had begun talks with Mr Rees and also government ministers who have approved about £100million in principle for the region's mass transit.

"I want to know why that hasn't come through yet, why are they prevaricating having made an initial agreement to give that money, so that will be an important part of getting things done," he said.

"We need to take this opportunity that Covid has given us and make the most of it.

"But a good public transport system is an awful lot of money and people will understand you need to get that money to produce the high-quality systems we want.

"So it's not going to happen overnight but I reckon that in 10 to 12 years we should have something that's really working well."

Mr Rees last month revealed that a shortlist of 19 options for a mass transit system had been seen to the DfT.

These are understood to have come from Weca, which Mr Norris is now in charge of, because the combined authority has responsibility for strategic transport in the region after powers were transferred from its three constituent authorities – Bristol city, South Gloucestershire and Bath & North East Somerset councils.

It is also not known how many of the 19 options include or did not include an underground which, if it becomes a reality, would be funded from a mix of government money and international investment sourced by the Department for International Trade.

Days after his election earlier this month, Mr Norris told BBC1's Politics West while sat opposite Mr Rees that "it may be that [an underground] isn't the answer, but if it is, then we're going for it".