Engineers working to raise a Machynlleth railway bridge out of a flood zone are battling through "extreme weather" conditions, they say.

Network Rail's project to raise Black Bridge, near Machynlleth, by one metre to protect the bridge from high river levels is now underway, with the line closed until June 28 to allow the work to be completed.

The bridge, which spans the river Dulas, sits precariously low to the flood plain and is frequently closed following periods of heavy rainfall causing disruption between Machynlleth and Shrewsbury.

Now, heavy rain at the end of May has caused the river levels to rise, hitting the closure mark of the bridge and Network Rail say, demonstrating why the work to lift the bridge is so important.

"The flooding we have seen at Black Bridge during our work shows exactly why raising the bridge is so important," said Kevin Giles, senior asset engineer for Network Rail Wales and Borders.

"During periods of heavy rainfall, the bridge is repeatedly flooded, causing regular closures on the Machynlleth to Shrewsbury route, leaving large sections of the Cambrian lines in central Wales isolated.

"We are putting passengers first by making the railway more resilient and reliable."

Additionally, the company says they have a limited time to get the work done due to environmental concerns in the fish-spawning River Dulas.

Despite these issues, Network Rail says work on the project is progressing well, with the bridge deck now secured into its temporary position until it is lowered on to its newly constructed bearings next week.

The railway will be closed until 28 June so that the work to raise the bridge and reprofile the track can be carried out safely, Network Rail says.

Transport for Wales are providing rail replacement services between Machynlleth and Shrewsbury.