Thousands of people were affected after members of the RMT union began the 48-hour stoppage on Wednesday over proposed changes to shift patterns.

Many services have been cancelled and others will operate on a reduced timetable and with restricted capacity.

The strike is due to run until Friday lunchtime, but fears have been voiced that the action could spread.

The RMT has warned that plans will be put in place next week for a ballot of signal staff across Britain.

The first rail strike in Scotland for nearly four years came after talks collapsed on Monday.

Nationally, the union and Network Rail agreed last July to introduce a 35-hour week.

The dispute centres on how that change will be implemented.

The RMT said the strike had been "rock solid" on Wednesday, when about 400 signalling and supervisory staff walked out at 1200 GMT.

How the strike has affected your region

General secretary Bob Crow said: "Network Rail should understand that our members are determined to achieve the 35-hour week we agreed to last July, and it is the company that holds a very simple solution in its hands.

"Network Rail now has the choice of engaging constructively with us to resolve this dispute or facing a ballot of our signalling members throughout Britain."

However, David Simpson, route director for Network Rail Scotland, labelled the action "regrettable" and "unnecessary" and insisted the company was willing to engage in discussions with RMT.

"We've offered to go to (arbitration service) ACAS to have this matter resolved, but RMT have refused that and passengers are suffering as a result," he said.

Train operator First ScotRail urged passengers to check its website to find out which services were operating.

No trains will run north of Stirling, and those operating further south will operate on a reduced timetable.

The Glasgow to Edinburgh service will run every 15 minutes every first hour and then every 30 minutes for the rest of the day.

Last trains will leave Edinburgh at 1745 GMT and Glasgow at 1800 GMT.

Extra buses have been put on standby in various parts of the country to cope with increased demand.

The Caledonian Sleeper service between Scotland and London is not running on Wednesday or Thursday, but should operate on Friday.