Business leaders predict a deal to ship Liquefied Natural Gas (LNG) to Pembrokeshire from all over the world will have major economic spin-offs.
They say it is a boost to the £1bn marine and shipping industry in the county that could see Milford Haven become the UK's third busiest port.
Hundreds of construction jobs will be created as the new terminal is build at the Petroplus plant in the town.
It should also create significant new business for suppliers and contractors.
It was announced on Wednesday that Malaysian company Petronas will import gas from around the world to a new terminal.
It will then be fed into to the UK gas supply in a deal worth a potential £4bn over 15 years.
Ted Sangster, chief executive of the Milford Haven Port Authority, said: "It's a very welcome boost to our traffic and also a very welcome boost to the Pembrokeshire economy.
"Skilled, well-paid jobs, are hard to come by in Pembrokeshire and the spin-offs from this announcement would be significant."
Milford Haven is currently the fifth busiest port in the UK handling around 3,500 ship visits a year.
Mr Sangster said Wednesday's announcement would increase traffic by around 7% with many of the ships needing supplies and maintenance when docking at the port.
"We have been working very closely with then in terms of the marine aspect and what sorts of ships they will use.
"They will be using ships towards the larger end of the ships we get at the moment.
Ted Sangster said it was excellent news for the county's marine sector
"But we are an existing oil and gas deep sea port with the infrastructure, systems and procedures to handle them."
The Port Authority estimates the marine industry, both through tourism and commercial shipping, is worth around £1bn to Pembrokeshire every year.
Pembrokeshire council's deputy leader John Allen-Mirehouse described the deal as excellent news.
"I understand that the next big announcement with be the awarding of the engineering contract to build the plant," he said.
"It is excellent news, not just for Pembrokeshire but for the economy of south Wales as it will guarantee a secure supply of competitively priced energy.
"This will give industries and businesses along the south Wales corridor a competitive advantage over their rivals."
But Friends of the Earth Cymru said they opposed the development.
Julian Rosser, director of Friends of the Earth Cymru, said: "One concern is about safety and whether these sorts of terminals should be close to centres of population.
"They don't tend to site them close to populated areas in North America.
"We also think that transporting gas like this is a step backwards in terms of energy efficiency."
The Petroplus plant is one of two LNG plants being built in Milford Haven.
The second is planned for the former Esso refinery.
LNG is natural gas cooled down to liquid form to make transportation more economical and easier.