EU referendum: Cameron and Jones join forces for Remain
Prime Minister David Cameron and First Minister Carwyn Jones have joined forces to urge voters to back remaining in the EU.
On a joint visit to British Gas offices in Cardiff, Mr Cameron said the referendum campaign was very close with many people genuinely undecided.
Mr Jones said Britain had to be "on the pitch" for the world to take notice.
Vote Leave Cymru said it was "another stage-managed event, organised away from real members of the public".
It is believed to be the first time the two heads of government - one Conservative, one Labour - have campaigned together.
Mr Jones was first to speak at the pro-Remain event on Wednesday, making his case for continued EU membership in football terms.
"Let's make sure we are on the pitch, let's make sure we are at the heart of Europe, and let's make sure people take notice of us," he said.
Mr Cameron said voters should not be suspicious of political rivals coming together on a common cause.
"When Labour and Conservative politicians are prepared to stand together on an issue .... I don't see that as some establishment stitch-up," he said.
"I see that as a reason really to listen to what is a very strong case that Britain will be stronger, safer and better off if we stay [in the EU]."
A spokesman for Vote Leave Cymru said it was "yet another stage-managed event, organised away from real members of the public", asking: "What are the remain camp afraid of?
"It's also highly unusual to see the Prime Minister sharing a platform with Carwyn Jones, having only recently declared that the most damaging thing for Wales' future would be another five years of Labour in government," the spokesman added.
"For Carwyn's part, during the general election he claimed that Conservatives at Westminster would do irreparable damage to Wales.
"It just goes to show how desperate the remain camp has become and they will say or do literally anything to instil fear in Welsh voters.
"The fact is, the safe choice is to vote leave on June 23 so that we can take back control of our own affairs and thrive and prosper as a truly independent nation."
Analysis by Nick Servini, BBC Wales political editor
This is a big moment in the EU referendum campaign in Wales and a clear attempt by the two men to try to rise above party politics.
Sharing a platform will be unpalatable for some in their respective parties.
After all, on the Labour side, Carwyn Jones has spent the best part of six years blaming a Cameron government for a huge range of problems.
And there is the deep-seated animosity between both parties that has developed over decades of tribal politics, from the miners' strike onwards.
There will be the fear in Labour ranks of the danger of sharing a platform with Conservatives, as has been seen in Scotland in recent years.
But, in the here-and-now, the question will be what can be achieved?
Many traditional Labour voters are going to vote to leave because they feel disengaged with politics and deeply concerned about immigration.
The leader of Welsh Labour sharing a platform with David Cameron is unlikely to change their minds.
But Labour itself admits there is confusion about the party's stance on the EU, and this appearance will help at least identify Labour with the remain cause.
Leave campaigners will inevitably see this as a desperate move by a campaign waking up to the reality of weakening public support.