Today's strike follows the first such strike in England in 40 years on January 12.
The walkout follows a breakdown of last-ditch talks between the British Medical Association (BMA), NHS Employers and the UK government's Department of Health over the shape of the new contract that all juniors in England will operate under from August this year.
The main sticking point remains payments for working on weekends and the government has argued the current arrangements are outdated and changes are needed to improve standards of medical care at the weekend.
"No doctor wants to take industrial action, and our door has always been open to talks. But the government is putting politics before reason, and their continued threat to impose a contract that junior doctors have roundly rejected leaves us with no option," the BMA said in a statement.
There are more than 50,000 junior doctors in England and the term covers those who are fresh out of medical school through to others who have a decade of experience behind them.
Talks between them and the government, hosted by UK's conciliation service ACAS, broke down at the end of January.
"If the BMA is prepared to negotiate and be flexible on that, so are we."
Ministers have repeatedly said that they reserve the right to impose the new contract should a deal fail to be reached.
But junior doctors have indicated they may be forced to resign if a new contract is imposed on them without an agreement on weekend pay.
