The Conservatives defended their record in government and claimed to be true party of Wales at their campaign launch on Gower.
Labour has promised to end "cuts and conflict" at an event in Ammanford.
Plaid Cymru launched their campaign near Llanelli on Friday while the Liberal Democrats' event will take place in Cardiff on Tuesday.
The five-and-a-half-week campaign is now officially under way after Parliament was dissolved under the terms of the Fixed Term Parliaments Act.
It is set to be one of the most closely fought election battles for years, with opinion polls showing no clear lead for any party, raising the prospect of another hung parliament.
Issues likely to dominate the campaign include the economy and spending cuts, Britain's EU membership and immigration.
Government ministers remain in charge of their departments until a new administration is formed but MPs will cease to be members of Parliament and writs will be issued for elections in all 650 constituencies.
Politicians hit the campaign trail in Wales as the starting gun is fired in a hotly-contested race for Number 10.