Some held banners reading "Edi Rama resign", while others featured a drawing of Albania's socialist prime minister handing over keys to Ivanka Trump, the US president's daughter.

The demonstrators argue that the estimated $1.2 billion project, led by Kushner and his wife Ivanka, will harm the environment, with plans for luxury hotels in the protected area of Vjosa-Narta on the southern coast.

According to the plan unveiled two years ago, the developers also hope to transform the island of Sazan -- formerly a communist secret military base -- into a glitzy tourist destination.

The protests have intensified in recent days after security guards assaulted a man near the protected area and footage of preparatory construction work and bulldozers on the beach was released.

The demonstrators want the repeal of the Strategic Investor Act intended to speed up certain projects, as well as a reversal of the changes to the Protected Areas Act allowing hotel complexes to be built in conservation zones.

Albania has 22 percent of its territory designated as protected areas.

Human rights activist, Luciana Kokaj, 31, explained that she owned a property in northern Albania that a "major investor" tried to seize with forged property titles.

"But this is beyond my personal interest: it's about protecting Albania for our children," she told AFP at the protest.

Fellow demonstrator Etleva Merko said that the protesters were "not against development of Albania" -- a rebuttal to Prime Minister Rama's accusations in recent days.

"We are for development, we are for transparency, we are against construction in protected areas," she insisted.

On Tuesday, the special prosecutor's office to combat corruption and organised crime said it had opened an investigation into the project, without revealing details.