Rail company Greater Anglia has urged passengers not to travel on their trains on Friday, or Thursday evening, unless their trip is absolutely vital as the big freeze continues.

Lines from Ipswich to Lowestoft and Felixstowe will remain closed because of problems with frozen track and points – which were difficult for engineers to reach because minor roads to the track were impassable.

On the main line to London and cross-country routes from Ipswich to Cambridge and Peterborough there will be some trains but journeys are likely to take longer than usual – there will only be one InterCity train an hour on the main line and service based on the Saturday timetable elsewhere.

More than 1,000 Network Rail engineers are working around the clock to try to keep the lines open – but it has so far not been possible to reach some of the more remote problems on secondary routes.

Regional director Steve Hooker said: “We had one problem at Kelvedon that took four and a half hours to fix because of the conditions – normally it would take 45 minutes.”

One issue they had to deal with was icicles starting to form on the wires above the track in Ipswich tunnel. Electric power had to be turned off for a time late on Thursday morning so the icicles could be cleared and trains could run again.

Mr Hooker added: “We are hoping to run a normal service again as soon as possible, but while these issues continue we can only do what we can. We are sorry for the inconvenience but we hope passengers understand the issues that we are facing.”

Trains from London to the region were taking longer than normal – a train on Thursday morning that was due to take just over an hour took two and a half hours. Passengers had to change at Colchester and the train was then held at Manningtree.

One passenger said: “It did take longer, but it was warm and it wasn’t overcrowded. We can see what problems there are and I think everyone seemed to accept that.”

Mr Hooker, who travels to work by train himself, said he had noticed a significant fall in the number of passengers during the week – suggesting that more commuters had been able to work from home or were taking a day off work. The cold weather is expected to continue until the weekend – but normal services should return next week.

Plans have been made to run the following service on Friday:

• A Saturday service will run on the Great Eastern mainline and some regional/rural routes: Norwich to London; Ipswich, Colchester, Chelmsford and all stations in between to London; Southend Victoria to London Liverpool Street; Norwich to Cambridge; Ipswich to Cambridge, Ipswich to Peterborough; Ipswich to Felixstowe; Harwich to Manningtree; Marks Tey to Sudbury.

• A shuttle service will operate between Braintree and Witham; Southminster and Wickford, Thorpe-le-soken and Walton-on-the-Naze.

• Stansted Express: three trains an hour, but with the usual weekday first and last trains.

• No service on the Norwich to Sheringham, Great Yarmouth and Lowestoft lines; and Ipswich to Lowestoft.

Jamie Burles, Greater Anglia Managing Director, said: “We apologise for the disruption to our customers. We are dealing with extreme weather which is causing problems to the railway just like on the roads.

“We have been trying to run the best possible service we can in these extremely testing circumstances. We’ve had extra people at stations helping to clear away snow and ice, making sure customers get on the right trains and de-icing train doors.

“But the extreme weather is causing problems, which is why we are taking this rare step of advising people not to travel unless absolutely necessary.”

Meliha Duymaz, Network Rail’s route managing director for Anglia said: “I know how difficult the past few days have been for people trying to travel by train.

“It has been extremely difficult to run a safe service on our rural lines but our teams have been out in difficult circumstances, working around the clock to keep as much of the railway running as best they can.

“We will continue to work with Greater Anglia to get all our services up and running as soon as we can, with the safety of passengers and our staff our number one priority.”

Snowdrifts blocking rails and icy temperatures freezing points and train doors have contributed to major disruption on the rail network.

Treacherous road conditions have caused difficulties for Network Rail and Greater Anglia staff trying to get to remote parts of the network to clear snowdrifts and access infrastructure such as signal boxes and points.

Customers should continue to check the Greater Anglia website, app and Twitter for the latest updates on the service. Weather forecasters are predicting rising temperatures over the weekend.