Members of the National Union of Journalists at the BBC are taking part in a two-day strike in a dispute over proposed changes to the pension plan.
The NUJ, which has 4,100 members at the BBC, voted to reject the BBC's "final" offer on pensions. Broadcasting union Bectu voted to accept the deal.
Radio 4's Today programme was cancelled, but the BBC News at Six and Ten O'Clock went ahead in full.
A further 48-hour strike is planned for 15 and 16 November.
The BBC has published a page detailing changes to the schedule due to industrial action.
The journalists' union said the action, which began at midnight on Friday, was having a "significant impact" on news and current affairs programmes.
NUJ general secretary Jeremy Dear said: "It is a clear indication that BBC journalists will stand up for a fair pension deal.
"Programmes that are going out are being run by freelance staff or managers, using pre-recorded packages.
"The strike is incredibly solid and the impact will grow over the course of the next two days."
But BBC director general Mark Thompson said in his blog: "We believe that much of the output on the BBC will be unaffected by this action.
"However, it is inevitable that some programmes and content will be disrupted.
"This has been a difficult period for staff. However, the people who lose out most in any strike action are the very people we are here to serve - our audiences."
NUJ members at the BBC are also set to observe an indefinite work to rule from Sunday, ensuring they take full breaks and only work their minimum prescribed hours.
The dispute stems from the BBC's plans to reduce a £1.5bn pensions deficit by capping increases in pensionable pay at 1% from next April.
Under the BBC's revised offer, the amount employees would have to pay into the pension scheme has been reduced from 7% to 6%.
In return, they would get a career-average benefit pension - based on the average salary over an employee's entire career - that would be revalued by up to 4% each year. The previous offer was 2.5%.
When employees draw their pension, payments will increase automatically each year in line with inflation, by up to 4% - again up from a previous offer of 2.5%.
Bectu, which represents technical and production staff, said after last month's ballot that the amended offer was "the best that can be achieved through negotiation".
But it added their position could be reviewed if the pensions deficit turned out to be less than £1.5bn.