NHS bosses say they will struggle to keep some pre-booked services going during the strike, as hospitals deal with a surge in flu and other winter illnesses.
The BMA said they would work with NHS bosses to ensure safety in hospitals and other parts of the health service.
At Prime Minister's Questions, Starmer said his message to resident doctors was: "Don't abandon patients, work with us to improve to conditions and rebuild the NHS."
In response, Conservative leader Kemi Badenoch claimed Starmer didn't "have the baubles" to ban doctors' strikes, and that he had lost control to trade unions.
Speaking at a picket line at a London hospital, BMA resident doctor leader Dr Jack Fletcher said that "we're here yet again, because we have not yet reached a credible deal to fix this absurd jobs crisis".
"What we're asking for is to stop these real-term pay cuts that the government is recommending for doctors," he said.
Asked about recent polling that suggests public support for the strikes is declining, he said: "I do care what my patients think but I didn't sign up to give that care in a corridor."
This is the 14th walkout by resident doctors in a long-running pay dispute.
The strike went ahead after last-minute talks between the government and union broke down without agreement on Tuesday.
The meeting was described as "constructive" by the government, but not enough progress had been made to call off the strike.
Resident doctors represent nearly half of the doctors working in the NHS. They are walking out of both emergency and non-urgent care with senior doctors drafted in to provide cover.