One of Africa's most ambitious energy infrastructure projects has finally been signed off at the highest level, with West African leaders formally endorsing the long-awaited Nigeria-Morocco Atlantic Gas Pipeline.

"Don't be surprised when the gas comes your way," quipped Julius Maada Bio, Sierra Leone's president and the current head of West Africa regional bloc Ecowas, following Sunday evening's ceremony in Freetown.

The vast 6,000km (3,700 miles) pipeline will run along the Atlantic coast of 14 African nations, carrying Nigerian gas to Morocco before linking into Europe's existing gas network via Spain.

Construction is expected to begin in 2028 with a total estimated cost of $25bn (£19bn).

It signals a change from current models where gas is typically extracted from African nations, refined and processed abroad then shipped back to African nations at three or four times the price, says energy expert and former Nigerian government advisor Charles Majomi.

That practice must end, because it is a "complete devaluation of the resource that is so fortunately endowed in places like Nigeria and other countries," he told BBC Focus on Africa.

By contrast, if leveraged correctly, the new pipeline has the potential not just to stimulate regional industrial growth but also boost Africa's power on the international stage.

"In terms of Africa's regional security and its ability to negotiate and have a seat at the global table, if you will, it does need this measure of usefulness to countries [in] Europe and Asia potentially," argued Majomi.

"Beyond energy security, it will open up Africa as a corridor to international markets," Prof Ganiyat Adejoke Adesina-Uthman, of the National Open University of Nigeria, said.

It is a symbol of what Africa can achieve when countries collaborate and work together, she added.

If all goes to plan a whopping 30bn cubic metres of gas per year will pass through the Nigeria-Morocco Atlantic Gas Pipeline serving 400 million consumers - making this one of the world's longest offshore gas pipelines and reshaping West Africa's energy landscape.

Sunday's agreement follows roughly a decade of negotiations involving more than a dozen countries. It establishes the legal and governance framework for the pipeline and is widely seen as the last major political hurdle before financing and construction decisions.

While construction has not yet begun, the project has entered a more advanced political and technical phase than at any point since it was first proposed in 2016.

The project is expected to be built in phases over several years rather than all at once, with analysts telling the BBC it will not begin in Nigeria because the country was initially flagged as a potential stumbling block.

"The plan is finance the project in segments starting with the Morocco-Mauritania-Senegal axis, then moving to the Ghana-Côte d'Ivoire axis... then the final connection would be to Nigeria which would then provide the gas," Majomi said.

Unlike the Trans-Saharan Gas Pipeline through Niger and Algeria, this Atlantic route largely avoids the Sahel's most insecure regions, although offshore construction significantly increases costs.

Feasibility studies are said to be complete, as are the front-end engineering design (FEED) studies. And the route that the pipelines will pass through have largely been agreed.

Financing may prove stickier - the projected $25bn cost could be pushed up by inflation, plus the success of a project of this scale relies on all 13 member nations (plus the disputed territory of Western Sahara) playing their part to protect the infrastructure from attacks.

"Whether or not a country will go into default on their off-take obligations for that gas as it moves [through] will be measured by their ability to muster security and integrate the host communities in helping to defend these long, long lines of gas pipelines. I think also leveraging the use drones and aerial monitoring situations will also come to bear," argues Majomi.

Nigeria's state oil firm and Morocco's national mining body are jointly leading the pipeline project. Regional institutions supporting the initiative include Ecowas, the ?Islamic Development Bank and ?the Opec Fund for International Development.

Beyond exports to Europe, it is intended to supply natural gas to countries that currently rely on expensive imported fuels, potentially supporting new power generation, fertiliser plants, petrochemical industries and manufacturing along the Atlantic coast.

For Nigeria, it offers an opportunity to monetise its vast gas reserves while strengthening economic ties across West Africa and North Africa.

Despite strong political momentum, significant obstacles remain. ?Financing the project and securing the pipeline route as well as ensuring political stability across participating countries will pose major challenges even before construction can advance.

Other challenges include the problem of long offshore engineering sections, plus the competition from other export routes - including liquified natural gas (LNG) projects and the Nigeria-Algeria Trans-Saharan Gas Pipeline.

Beyond all of these, is the questions over future European gas demand as the continent accelerates its transition to renewable energy.

"Nigeria has the gas and there's market access from Morocco to Europe. It's not just a extracting energy, it will lead to access to clean energy for many countries with Morocco is a gateway," says an optimistic Prof Adesina-Uthman.

"It will also create industries, job opportunity and ultimately a global market. It's not just for regional integration but a global project."