Members of the British Medical Association (BMA) in England are staging a fifth round of strikes, walking out for a full 96 hours from 7:00 a.m. (0600GMT) on Friday until Tuesday morning.
The BMA members are also expected to hold a demonstration in central London later on Friday.
Britain's Health National Service (NHS) has warned that some services will be affected due to the strike action throughout the day.
Earlier, the government declared that it had presented a "final" pay offer to junior doctors, and British Prime Minister Rishi Sunak asserted that further negotiations would not take place.
As per the current offer, junior doctors are set to receive a 6% pay increase, plus £1,250 ($1,585). This raise translates to an overall pay hike ranging from 8.1% to 10.3%, depending on their previous pay packages.
However, the British Medical Association (BMA) has expressed its disagreement, saying that Sunak cannot unilaterally decide that negotiations have concluded without engaging in direct discussions with the union.
The core demand of the association is the restoration of their salary to the level equivalent to what they earned in 2008, reflecting a 35% increase.
Last month, senior doctors across England held a 48-hour strike for the same reason, marking their first industrial action since 2012.
The UK has faced several strikes and protests by the NHS staff over pay disputes and working conditions. Lack of workforce resulting in long waiting lists at A&E services are among the complaints made by the public and staff alike.
In a speech this January, the British premier said cutting waiting lists is one of the top five priorities of his government.
In a bid to resolve problems the NHS faces, the government unveiled a 15-year workforce plan in late June