The Anglesey AM and Deputy First Minister Ieuan Wyn Jones says closing Holyhead coastguard station will put lives at risk.
Mr Jones, also the Plaid Cymru leader, spoke as he visited the station to support its coastguard teams.
The site faces closure, along with Milford Haven's coastguard station as part of UK government cuts.
The Maritime and Coastguard Agency (MCA) has said that operations need to be more effectively run.
It would leave Wales with just one coastguard base at Mumbles near Swansea.
"The UK government's proposal to close the station and leave the Anglesey and north west Wales coastline without 24 hour local cover would put lives in danger," said Mr Jones.
"Local knowledge of the coastline and place names is vital in terms of rescue times and it is therefore important that the station in Holyhead is kept open."
Mr Jones said he was also seeking views from the island's residents on whether they felt powers over coastguard services in Wales should be devolved to the assembly.
"I am anxious to hear how local people feel about this much needed public service and how it can be best run in Wales, for the benefit of the people of Wales," he added.
Under proposals outlined by Shipping Minister Mike Penning in December, there will be three 24-hour operational centres - at Aberdeen, in the Southampton/Portsmouth area and at Dover.
In addition, there will be five sub-centres open during daylight hours - at Swansea, at Falmouth in Cornwall, at Humber in Yorkshire and at either Belfast or Liverpool and at either Stornoway or Shetland in Scotland.
On Tuesday, more than 100 people took part in a demonstration in Pembrokeshire against the closure of the Milford Haven station.
The protest marked 15 years since the Sea Empress oil tanker disaster nearby.
A rally against the proposed closure of the Holyhead base will take place on Saturday, organised by Labour Party activists and the PCS union.
The MCA is going through a public consultation process on the proposals, with public meetings at all three Welsh stations taking place in the first week of March.
Vice Admiral Sir Alan Massey, the head of the service, said when he was in Milford Haven earlier this week: "What we are seeking to achieve is a better coastguard service in the 21st Century and to do that we need a national network and to make better use of the people, skills and technology so we can coordinate things to be far more efficient than we are at the moment.
"Local knowledge is a key issue and seems to be the one that captures people's imagination, but we have to be more analytical.
"We need to use our data systems more efficiently and use those who have detailed local knowledge in a better sort of way."