Librarians and social workers are among those on strike in Manchester
Thousands of council staff are striking over pay in their biggest campaign of industrial unrest for years, forcing schools to close and hitting services.
Employers say 100,000 Unison and Unite members in England, Wales and N Ireland have joined the 48-hour action - but the unions put the figure at 500,000.
Unions say the rising cost of food and petrol effectively makes a 2.45% pay offer a pay cut, and they want 6%.
Council employers say they have reached the "limit of what is affordable".
Meanwhile, members of the Public and Commercial Services Union (PCS), who include driving test examiners and coastguard control room staff, are also striking in a separate row over their below-inflation pay offer.
The union estimates up to 5,000 driving tests across the UK may have been cancelled by the end of Wednesday.
Town hall services
The Local Government Association (LGA), the organisation representing local councils, said it estimated that about 8% of the workforce directly affected by the pay dispute was on strike - or just over 100,000 people.
The pounds in local government workers' pockets are turning to pennies
Unison general secretary Dave Prentis said more than 250,000 of its members earned less than the basic rate of £6 per hour.
"The pounds in local government workers' pockets are turning to pennies," he said.
"The cost of everyday essentials like milk, bread, petrol, gas and electricity are going through the roof - our members cannot afford to take another cut in their pay."
Unite national officer Peter Allenson said its members were "living on the breadline".
But one council worker in south-east England, who broke the picket line and did not want to be named, said the pay offer was good in the "current economic climate".
"In local government we are guaranteed a pay rise every year and over the last 10 years, it has varied between 2.5% and 3% - people in the private sector don't get anywhere near that."
The RPI inflation measure - often used as a benchmark in pay negotiations - is currently 4.6%.
Jan Parkinson, managing director of Local Government Employers (LGE), which was created by the LGA in 2006, said: "Our greatest asset is our staff but we have simply reached the limit of what is affordable.
Council workers on strike
"We remain willing to talk to the unions on a constructive basis about the future employment conditions of our workforce but this week's strikes will not change the fact that our last offer was our final offer."
John Ransford, LGA deputy chief executive, said councils would have to put up council tax or cut services in order to meet the pay demand.
In the PCS union dispute, more than 1,500 members working for the Driving Standards Agency (DSA) across the UK are taking take part in a one-day strike over pay.
And about 2,500 Valuation Office Agency staff in England and Wales are working to rule on Wednesday and Thursday.
On Friday, about 10,000 Home Office staff, including immigration officers, are expected to go on strike, while about 5,500 Land Registry workers in England and Wales only are due to walk out on Friday afternoon.
Coastguard control room staff around the UK are set to strike for 48 hours from Friday.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.