Much of the West Country was paralysed by snow chaos on Friday as normal life was brought to a standstill by the extreme wintry conditions again.

Giant falling sheets of ice prompted authorities to close both Severn Bridge crossings in an unprecedented move which symbolised the West's big freeze and another day of turmoil on our transport network.

The M48 crossing did reopen later in the day but, by that time, the snow crisis had struck everything from electricity supplies, schools and hospitals to public transport, airports, roads and rubbish collections.

And the chaos looks set to continue well into next week with forecasts of plummeting temperatures and freezing conditions over the weekend as local councils run out of salt and grit to treat the roads. Gloucestershire County Council has been promised 500 tonnes of table salt on Sunday, which it will use to grit the roads in an extreme effort to get the county moving.

Some local authorities told residents not to even venture out, as the freeze sparked what is effectively a state of emergency in many parts.

The severe weather left 21,000 West homes without power last night.

About 8,000 in Taunton were cut off. The closure of both Severn Bridges hampered efforts to restore the supply. Emergency volunteers ferried nurses and doctors to work using 4x4s, while police drivers closed roads, turned drivers back and scoured rural lanes looking for stranded motorists.

Great Western Ambulance Service was called to 10 crashes in less than three hours early yesterday morning, including incidents in Coleford, Rowberrow in North Somerset, Chippenham, Dilton Marsh near Bath, Cheltenham, Weston-super-Mare, Hucclecote and South Cerney in Gloucestershire, Chepstow and Tewkesbury.

A man was taken to hospital in Swindon with head injuries after seven youths assaulted him when he challenged them for throwing a snowball at his car in the town centre. Flights were cancelled at Bristol airport for much of the day, disappointing 100 stranded Welsh rugby fans who were hoping to fly to Edinburgh for the Six Nations opener.

Vital deliveries to supermarkets were delayed as about 50 lorries were stranded at the roadside on the A37 in Bristol for eight hours as they struggled to make it through snow.

Motorists venturing across the Severn Estuary faced a 100-mile detour along the snow-covered motorways of Gloucestershire, while the Highways Agency worked to knock ice off the frozen overhead gantries.

Five cars had their windscreens smashed by falling blocks of ice, some a metre across, on the Second Severn Crossing – and the original Severn Bridge was also closed as a precaution. There were no reports of injuries.

The TaxPayers' Alliance criticised transport authorities over the closing of the Severn bridges, saying they "failed to prepare". Campaign director Mark Wallace said: "I think it's amazing that, given the technology involved in building something like the Severn Bridge, a snowstorm can simply shut it down."

But bridge boss Jim Clune said: "It's very much a safety hazard and, of course, these gantries span all carriageways on the motorways."

As councils continued to ration salt and grit stocks, major A-roads were closed and traffic struggled to slither around the motorway network in the region.

The snowfall began at about 11pm on Thursday night and continued well past lunchtime yesterday, from Somerset and up into Gloucestershire.

In Bristol, public-spirited passers-by came to the rescue when an ambulance got stuck. The crew was on its way back to the station when snow and ice halted them in Downend. One man arrived with cardboard and a shovel. When this was unsuccessful, he disappeared, only to return a short time later alongside a gritting lorry he had flagged down. Despite the lorry being almost empty, bystanders off-loaded the remnants onto the road. It worked and allowed other motorists to make it up the hill safely.

The Conservatives said the chaos showed the Government should have done more to prepare for the wintry weather, as council chiefs across the region begged for Government intervention in the face of the crisis.

"It is alarming that we face a grit shortage," said shadow transport secretary Theresa Villiers. "If grit starts to run out this will have deeply worrying implications for road safety as well as leading to gridlock for those trying to get to work."

Shadow local government spokeswoman Caroline Spelman said: "The Government need to get a grip as Britain's grit crisis worsens. Labour ministers are in denial – there is hardly enough salt to grit our motorways, let alone side streets and pavements. People are being put at risk of serious and minor injuries as a result, whilst the elderly and less mobile are being forced to stay in their homes."

The row over the salt shortage led to councils begging for supplies from each other.

Gloucestershire and Wiltshire are worst affected. Councillor Stan Waddington, Gloucestershire's man in charge of roads, accused other councils of being stingy.

He said: "We know that there are some councils who have salt available – salt that we desperately need. At the moment we are unable to convince these councils to release just a small amount of their supplies, which would keep Gloucestershire moving until the national crisis is over."

But Lib Dem councillors in the county accused Tory council chiefs of incompetence. "The situation here now appears to be more desperate than previously reported by the council. Staff in our county highways teams worked hard throughout the night, but they are running out of salt. Other councils are not in this situation," said Lib Dem leader Jeremy Hilton.

The situation is set to worsen as forecasters predict plummeting overnight temperatures as low as -10°C this weekend.

Weather experts are warning the slushy snow on the West's roads will turn to ice, leaving driving conditions worse than ever, with snow showers continuing.