Doctors are taking industrial action for the first time in almost 40 years.
Medical staff across Scotland have suspended all non-emergency services in protest over pension reforms.
The BMA said that it was working closely with the NHS to minimise disruption, but hundreds of non-emergency appointments have been cancelled as a result of the action.
However, doctors are attending their usual practices and workplaces and will be available to conduct emergency procedures.
In a statement, the BMA said: "The latest changes will see doctors paying up to 14.5% of their salaries in pension contributions - twice as much as some other public sector staff on a similar salary in order to receive a similar pension.
"They will also have to work longer to receive their pension - up to 68 for younger doctors."
Scottish Conservative Health Spokesman and Deputy Leader Jackson Carlaw MSP said the doctors were "damaging their reputation" by taking action.
He said: "The many patients who should have been undergoing procedures tomorrow are the ones who should be at the forefront of our minds.
"It will be them tomorrow, but could easily have been any of us. Doctors risk damaging their reputation over this action, and once that reputation is lost with patients it is very hard to regain.
"We are in no doubt this action will prove ineffective and pointless."
The action follows a 24-hour strike by non-medical BMA staff on Wednesday.