Downing Street warned the public that the coordinated strikes would cause “significant disruption” as around half a million workers across the public sector stage a walkout over pay, jobs and conditions.
The National Education Union (NEU) estimates around 23,000 schools are being affected by strike action across England and Wales, with up to 200,000 members taking to the picket line.
Some 150 universities are also being affected by strike disruption on Wednesday as lecturers and librarians belonging to the UCU union join the walkout.
Up to 100,000 members of the Public and Commercial Services union (PCS) are thought to be striking across government departments, Border Force, museums and other government agencies.
Meanwhile, train driver members of Aslef and the Rail, Maritime and Transport (RMT) union are walking out on Wednesday in a long-running dispute over pay, jobs and conditions.
Industrial action is affecting the 14 biggest rail operators in the UK, and has brought most services to a grinding halt.