Snow causes more than 300 Essex schools to be closed
More than 350 schools are closed in Essex, mainly in the central and southern parts of the county.
Motorists have also been urged by police not to take "unnecessary risks" as road crashes are causing problems.
A crash blocked the southbound A130 at Great Baddow and the Army and Navy Flyover at Chelmsford is closed by ice.
Both Dartford crossing tunnels have now been closed at junction 30 on the M25 after the bridge crossing, closed overnight, reopened at 0700 GMT.
Sixty-five gritter lorries are operating at "full strength" to treat more than 1,800 miles of the county's main roads, the council said.
Motorists are facing long delays because of congestion caused by snow on a number of main routes, including the M25 and A127.
However, there are long tailbacks on the M25 going south and the car park at Thurrock Services is full of cars left overnight.
A jackknifed lorry on the clockwise section of the M25 at junction 28 is adding to traffic problems in the area.
Ch Insp Richard Phillibrown, head of road policing in Essex, said things were slowly starting to improve on the motorway and surrounding roads.
Temperatures fell to -4C (25F) overnight, with widespread ice affecting roads.
Stansted Airport open
"The county council is required to focus its gritting resources on keeping major roads clear, so it operates a precautionary salting network," a spokesman said.
"This includes all A and B roads, access routes for emergency services, rural link roads and major public transport."
Forecasters said most places in Essex should remain dry on Wednesday.
Stansted Airport has not closed during the current cold snap but has advised passengers to contact their airline for updates.