Australia and New Zealand have informed organisers in England they are pulling out of the 2021 Rugby League World Cup, citing "player welfare and safety" during the Covid-19 pandemic.
The world's top two ranked nations - who between them have won the last nine editions of the Rugby League World Cup - issued a joint statement urging organisers to delay the tournament until next year.
They said the decision to withdraw came after considering the risk of infection in England, the worsening coronavirus environment in Australia and the time most players would be away from home under strict biosecurity conditions before the World Cup.
"Not participating in this year's World Cup is not a decision the Commission has taken lightly, but we must put the best interests of our players and officials first. Protecting them is our absolute priority," Australia Rugby League Commission boss Peter V'landys said.
"In the current environment, the risks to the safety, health and wellbeing of the players and officials travelling from Australia to participate in the tournament this year are insurmountable."
New Zealand Rugby League chief executive Greg Peters said the decision to withdraw was in the best interests of players and officials.
"There are stark differences between how the pandemic is being managed in the UK compared to Australasia and recent developments have highlighted how quickly things can change," he said.
"The tournament organisers have moved heaven and earth to make this work, so it is not an easy decision, but the Covid-19 situation in the UK shows no sign of improving, and it's simply too unsafe to send teams and staff over."
About half of Australia's population has been placed back into lockdown following a spike in Covid-19 cases, with stay-at-home orders now in place in South Australia, Victoria and parts of New South Wales.
That is in sharp contrast to England, with the majority of coronavirus restrictions now lifted.
The UK reported 44,104 cases on Wednesday following the government's easing of restrictions on Monday. The World Cup is scheduled to open on October 23.
Defending champions Australia were to play Fiji in Hull on the opening day, with New Zealand drawn to play Lebanon in Warrington the following day.
A statement from the tournament organisers read: "RLWC2021 note the disappointing statement made by the ARLC and NZRL which may have wide ranging implications for international Rugby League.
"RLWC2021 were informed at very short notice and will continue discussions with all stakeholders to agree on the best way forward. A further statement will be made in due course."