Leaving the EU without a trade deal could kill off advanced manufacturing in Wales, the first minister claimed in a speech to the Labour conference.
Carwyn Jones announced £6m worth of grants for Ford, Toyota and Airbus to help the big employers deal with the effects of Brexit.
Mr Jones warned that a hard Brexit could bring a "new wave of industrial carnage".
He blamed the prospect on the Conservative UK government.
The announcement came as he revealed he may nominate Eluned Morgan to ensure the Welsh Labour leadership contest is not all male.
At the Labour conference - his last before standing down - Mr Jones said a hard Brexit would mean "a new wave of industrial carnage with a real risk to advanced manufacturing".
His speech in Liverpool said the prospect of a "catastrophic" no-deal Brexit is the fault of the "paralysis and incompetence of this Tory Government".
Theresa May's Chequers plan would have been a "viable starting position" two years ago, but "not with weeks of negotiating time left".
The money for the three manufacturers will come for an EU Transition Fund, set up by the Welsh Government earlier this year to help employers minimise the disruption of Brexit.
It is meant to pay for technical and commercial advice, and help companies continue to attract EU workers.
The conference has been dominated by discussion over whether Labour should back calls for another referendum on the final Brexit deal.
On Tuesday the conference will vote on whether to keep "all options on the table" on Brexit, including possibly campaigning for a new referendum.
Party members have called for another referendum and while leader Jeremy Corbyn has said he would prefer the issue to be resolved by a general election, he has said he will adhere to whatever the conference decides.
The first minister has previously said a referendum should only happen if parliament rejects the final deal and if Mrs May is forced into a general election.
Mr Jones is expected to hand the reins to a successor in December.