Public health bosses say they hope to start reducing restrictions “very quickly” on a 12-mile stretch of canals in the West Midlands following a toxic chemical spillage.

Sodium cyanide, which can cause seizures, vomiting and loss of consciousness, was confirmed on Tuesday as the chemical spilled into the waterway in Walsall.

People have been urged not to go near a long section of the canal network and towpaths from the middle of the borough to Birmingham and including connected waterways in Wednesbury, Tipton and West Bromwich.

The authority’s interim director of public health, Nadia Inglis, said they were “doing things cautiously but as quickly as we can”.

“We’re testing all points of that affected area currently and we’ll be reviewing those result as they come through,” she added.

“We’ll be removing those restrictions and hopefully reducing the size of that potentially affected area where we are confident there isn’t a risk to health.”

The exclusion zone markers run from the Walsall lock flight to lock flights at Rushall/Ryders Green in the borough and Perry Barr in Birmingham.

On Tuesday, council leader Garry Perry said it was too early to speculate how the substance entered the waterway but promised regular updates as a major incident was declared.

Sodium cyanide dissolves in water and can have serious adverse health effects if people or pets come into direct contact with it, the council advised.

The chemical, a white crystal-like solid with a faint almond odour, is used in industry for metal cleaning, plating and extraction, and photography.

The UK Health Security Agency said exposure could cause symptoms including headaches, nausea, dizziness, loss of consciousness, seizures and vomiting.

Anyone exposed to the water who felt unwell should seek medical advice through the NHS 111 service or phone 999 in an emergency, a spokesperson for the authority added.

Ms Inglis added: “Our primary aim has been to keep the public safe and to protect their health and wellbeing.

“Given the nature of the substance, we’re taking a cautious approach to protecting our public until we know it’s safe to open those canal towpaths again.”