Labour has a "mountain to climb" in the snap general election, First Minister Carwyn Jones has said.
Mr Jones made his first appearance since the announcement of a poll for 8 June was called earlier this week.
Campaigning in Bridgend, Mr Jones said his party would need to tailor its message according to which nation it campaigns in.
"What the Tories offer is the same old," he said. In response the Tories said it had the leadership to deliver.
One YouGov UK opinion poll in the Times on Thursday suggested Conservative support was at 48%, with Labour on 24%.
The first minister has previously said that it would be 'tough' for Labour to avoid council poll losses.
MPs voted on Wednesday to trigger a general election on 8 June. All 25 existing Labour MPs will be standing.
The AM for Bridgend said Prime Minister Theresa May "seemed to be making the election about Brexit" - he believed it was about the state of public services in England.
"There's a mountain to climb, there's no doubt about that," he told BBC Wales.
He said things were not easy for Labour, but the party had faced "very great difficulties in the past".
"Jeremy (Corbyn) is leading the campaign and I will be with him when he comes to Wales," he added.
Mr Jones said he could see the Labour leader walking into 10 Downing Street, adding that Mr Corbyn had to "prove himself".
Asked if there would be clear red water between Welsh Labour and UK Labour, he said: "No, I think it's a question of tailoring our message according to which nation we're campaigning in.
"My worry is that the Tories will use this in a way to squash the three Celtic nations. They are pretty power hungry.
"The people of Wales need to send them a message that they are not going to be walked over."
Welsh Conservatives leader Andrew RT Davies said: "Conservatives in government have done more than any other party to transfer greater powers to Wales, with the latest Wales Act as the most recent example."
He claimed Mr Jones' comments displayed a "wilful ignorance of the facts".
"A vote for Labour is a vote for the more borrowing, more debt, a chaotic Brexit, and weakened defences," he said.
"Only Conservatives have the vision, leadership and strong economic record needed to deliver on Wales and the United Kingdom's national interests."
Plaid Cymru Westminster leader Hywel Williams said his party did not want a repeat of the EU referendum campaign.
"The question really is how do we make sure how Wales benefits from the new situation," he said on BBC's Good Morning Wales.
"It's not a referendum anymore. Bad generals fight the last war.
"We've got endemic poverty. We've got a lack of imagination and energy in the government in Cardiff and the government here in London doesn't really bother about us unless we make a lot of noise."
He said he would be "delighted" if Plaid leader Leanne Wood stood in the Rhondda.