The United Kingdom government's plan to send some migrants to Rwanda cleared a major hurdle early Tuesday, when lawmakers formally declared the African nation "safe".

The proclamation addressed a Supreme Court ruling that had prevented deportations over concerns the nation was unsafe.

Prime Minister Rishi Sunak welcomed Parliament's decision and said the UK will start sending a percentage of all illegal arrivals to Rwanda within 10 to 12 weeks.

"The passing of this landmark legislation is not just a step forward but a fundamental change in the global equation on migration," he said. "We introduced the Rwanda Bill to deter vulnerable migrants from making perilous crossings (of the English Channel in small boats), and break the business model of the criminal gangs who exploit them. The passing of this legislation will allow us to do that and make it very clear that if you come here illegally, you will not be able to stay."

Hours after Parliament's decision, the danger of that "perilous crossing" was underlined when at least five people died while trying to cross the 34-kilometer-wide stretch of water.

"We will start the flights and we will stop the boats," Sunak insisted during a Downing Street news conference.

The UK has been grappling for years with the illegal arrival of people in small boats. Around 30,000 migrants are known to have made their way to the country that way last year. And, so far this year, another 6,000 have done so.

The country has said it does not have adequate space, accommodation, and services to welcome everyone who wants to live there. But the challenge has been finding humane ways to stop the boats from arriving. Sunak and his government are hoping the Rwanda Bill will deter economic migrants, while leaving the door open to genuine refugees fleeing persecution and war.

But charities and organizations that work with refugees have criticized the legislation and demanded better solutions.

The opposition Labour Party's shadow home secretary, Yvette Cooper, described the plan as nothing more than an "extortionately expensive gimmick" that will do nothing to "tackle dangerous boat crossings".

The United Nations said it will have a harmful impact on refugee protection and human rights around the world.

In a joint statement, UN high commissioners Filippo Grandi and Volker Turk urged the UK to think again and said all countries must uphold their obligation to accept and help people seeking asylum.

The campaign groups Amnesty International, Freedom from Torture, and Liberty said in a joint statement the Rwanda Bill "trashes … international law whilst putting … refugees at risk of an unsafe future".

The UK first unveiled its Rwanda plan two years ago, when Boris Johnson was prime minister.