The action has been called as a response to falling prices and the government's handling of rural issues. Farmers taking part have been asked not to sell whatever they produce during the day even if it means it will go to waste.
At the same time, protesters were due to deliver hampers of UK-grown produce to Number 10, the Scottish executive, Welsh assembly, and Northern Ireland assembly to illustrate what is at stake.
No one is sure how many of the 352,000 UK farmers will take part in the 24-hour strike.
Farmers For Action, the group organising the protest which started at midnight, claim it could be as many as 20%. The strike does not have the support of the powerful National Farmers' Union (NFU), who described it as a "risky strategy that could backfire".
The National Beef Association said they would not go as far as supporting the strike but understood the pressures farmers were facing.
Livestock auctions are unlikely to be affected as none handling meat for slaughter is scheduled to take place and just four official farmers markets are planned, all of which report no disruption.
David Handley, chairman of Farmers For Action, said they would be calling on environment, food and rural affairs secretary, Margaret Beckett, to resign for failing to properly address problems faced by farming.
Mr Handley, a dairy farmer from Monmouthshire, said: "It looks like support for the strike will be in excess of 20% judging by the phone calls to the office.
"As far as we are concerned there is a plan to reduce the number of producers in the UK and we think this is to the detriment of the country because we need to be self-sufficient."
He said the one-day strike was designed to illustrate the importance of agriculture to everyday life and warned unless their concerns were addressed direct action could follow.
Mr Handley, a veteran of the fuel protests of 2000, said the same tactics, as well as those used by militant French farmers, may be employed.
Meanwhile, a spokeswoman for the NFU said: "We are working in numerous ways to improve the dire situation but there is no magic wand to make things better overnight.
"We think this is an extremely risky strategy that could seriously backfire. If it results in a single extra French apple or Argentinian steak on British supermarket shelves because they can't get hold of home-grown food then it will have done more harm than good."
