London, England (CNN) -- Snow and freezing temperatures hit large parts of Britain Wednesday, forcing airports and railway lines to close down, and forecasters warned that more bad weather was on the way.
Most of Britain was covered in snow, with 20 to 30 centimeters (nearly 8 to nearly 12 inches) of snow in the southern parts, and up to 15 feet in the Pennines, the mountain range that runs from northern England north to Scotland.
Four airports, including London's Gatwick, were shut down because of snow and ice.
Gatwick said 84 flights were canceled, mainly on British Airways and EasyJet. Bristol, Blackpool, and Exeter airports were also closed.
British Airways was forced to cancel "dozens" of flights in and out of London's Heathrow Airport Terminal 5 due to snow and ice, a spokesman told CNN Wednesday.
Both incoming and outbound flights were experiencing significant delays, the spokesman said.
BA operates about 400 flights a day in and out of Terminal 5, the airport's newest wing.
According to BAA Limited, the company that operates the British airports, Heathrow "overall is fine," as the facility was alternating runways to keep cancellations to a minimum.
Stansted Airport in north London was briefly closed but reopened at midday. Still, it reported 27 flight cancellations.
Manchester Airport, which was shut Tuesday, was reopened. Officials said snow was unlikely to affect flights, but warned travelers to expect delays because of Tuesday's flight cancelations.
All major train lines were open, but some train operators were running restricted services because of the weather. They included South West Trains, which runs services between London and some of the hardest-hit areas, such as Hampshire, Surrey and Wiltshire, and Chiltern Railways, which runs between London and Birmingham.
Virgin Trains said it planned a regular service, but it warned of the risk of delays and cancelations on routes between London and Birmingham, Manchester, Liverpool and Scotland.
Trains in northern England and Scotland were suffering because of the snow. There were no services between the Scottish cities of Inverness and Perth, National Rail said, and no trains between the English cities of Sheffield and Leeds.
Britain's Highways Agency warned of difficult driving conditions in central southern England and the north of the country. It urged drivers to delay non-essential trips.
Dozens of cars were left sitting on the side of the road in Southampton, near England's southern coast, after drivers became stuck in snow.
The Highways Agency warned drivers to avoid the nearby A3 highway, which runs between London and Portsmouth, because of weather conditions.
The agency said it was doing continuous salt treatment and snow plowing on major roadways in England.
Schools were closed across the country because of the heavy snowfall.
Officials said 176 schools were shut in Buckinghamshire and 164 were closed in Oxfordshire just to the northwest of London. About 330 schools in Gloucestershire, 200 in Somerset, and 143 in Wiltshire were closed because of snow, officials said.
Hundreds of schools were also closed in Kent, Shropshire, Herefordshire, Worcestershire, Coventry, Bath, Windsor, Maidenhead, Liverpool, and Brighton, officials said.
The Met Office, Britain's weather service, said more snow was expected Wednesday for southern and northeast England. It warned of "very heavy snowfall" in southwest and southeast England and London, with up to a foot of snow possible.
CNN's Laura Perez Maestro and Phil Han contributed to this report.