Reform UK has announced plans to close down the UK's asylum system for a full parliamentary term if it were to enter government.
The party said all new asylum applications would be rejected and existing applications voided, with all claimants marked for deportation, which Reform said would effectively suspend the asylum system.
Reform would scrap the asylum tribunal system, which hears asylum appeal cases, and claimants in more than 90,000 outstanding appeals would be deported.
It said no grants of humanitarian protection or refugee status would be made.
Labour chairperson Bridget Phillipson called the proposals a "clear sign of desperation and weakness".
"Running away from basic decency by entirely abandoning those escaping war and persecution might look to Reform like a way of winning a bidding war with other parties on the right, but the vast majority of British people will reject it as an assault on our common values," she said.
Conservative shadow home secretary Chris Philp said the proposals "largely copy" his party's policies, arguing: "Only the Conservatives have a serious and credible plan to fix our borders."
Liberal Democrat home affairs spokesperson Max Wilkinson said: "Reform and the Conservatives were the architects of the failed asylum system and now they will exploit it at every opportunity - including Farage's latest announcement."
Reform said it would pull the UK out of the European Convention on Human Rights (ECHR), repeal the Human Rights Act 1998 and disapply the 1951 Refugee Convention to prevent legal challenges to its plans.
Party leader Nigel Farage said the UK is "facing a national security emergency" and "we cannot accept more asylum seekers while we still have no idea how many people are in the country illegally and the threat they pose."
Home Office staff who currently oversee asylum claims would be "reprioritised to reviewing and overturning previous refugee grants", Reform added.
The party said it would attempt to pressure other countries into accepting those marked for deportation from the UK by using visa bans and tariffs on goods and services.
Pakistan, Somalia, Eritrea, Syria, Afghanistan and Sudan could be hit with visa bans under these measures.
If these policies are unsuccessful, Reform would "apply further sanctions, including banning a country's airlines from British airspace and their citizens from transit", the announcement added.
In "extreme cases" where no country is willing to take custody of a deportee or it is inappropriate to return someone to their home country, Reform said it would negotiate deals with third countries.
In April, Reform pledged an immediate review of all asylum claims from the last five years should the party win the next general election.
Around 400,000 people would be liable for deportation under the plans, which would target anybody granted asylum, overstaying a visa, or from a country deemed safe by a Reform-led government.
The party previously announced it would bar anyone arriving on a small boat, and suggested this could mean 600,000 deportations over five years.
Both Labour and the Conservatives have also pledged to make changes to the asylum system.
Phillipson said Farage is "casting around for more and more extreme policies" as he deals with questions about finances and rival party Restore Britain.
Phillipson said Labour is showing "we can control immigration and get numbers down with serious action, not by abandoning the asylum system altogether", adding that "right approach" is "not giving up or caving to the most extreme voices, but ensuring that the rules we have are properly enforced".
In March, Home Secretary Shabana Mahmood said any asylum seeker given refugee status will now only be offered temporary protection, reviewed every 30 months.
In September, she also reopened a scheme to resettle refugees in the UK, saying she hoped that offering "safe and legal" routes would deter small boat crossings.
The Home Office said the UK Resettlement Scheme (UKRS) would reopen immediately and expected that around 25% of arrivals would be Afghan women and girls and Palestinians.
Philp said Reform's plans mostly mirror Conservative policy from a year ago, including banning asylum claims by people who entered the country illegally, abolishing the immigration tribunal, ending Labour's resettlement routes, and leaving the ECHR.
The Tories previously said they would task officials with removing 750,000 illegal immigrants within five years, under Trump-style deportation plans.
Lib Dems spokesperson Wilkinson said the "UK can only restore order, control and fairness by joining the EU migration and asylum pact", which increases the number of irregular migrants returned to their home countries and spreads responsibility for asylum seekers across the EU.