Prosecutors from several US states on Wednesday unveiled a sweeping proposed settlement under which four pharmaceutical companies accused of fuelling the country's opioid epidemic would pay up to $26 billion to resolve some 4,000 claims in federal and state courts.

Under the proposed agreement, three drug distributors -- McKesson, Cardinal Health and Amerisource Bergen -- along with drug-maker Johnson & Johnson, would pay to resolve the claims, as well as finance prevention and treatment programs, said a press release from New York Attorney General Letitia James, who was joined on a briefing by prosecutors from six other states.

The proposed settlement is the largest unveiled thus far in the multi-year effort in courts to hold the industry accountable for the opioids crisis, which has caused more than 500,000 deaths in the United States in the last 20 years. 

"The numerous companies that manufactured and distributed opioids across the nation did so without regard to life or even the national crisis they were helping to fuel," James said in a statement.

"Today, we are holding these companies accountable and infusing tens of billions of dollars into communities across the nation, while taking significant steps to hold these companies accountable."

James told a briefing with reporters that the settlement covers civil cases but was silent on criminal liability. She declined to comment on whether any criminal charges were still possible. 

At least two states, Washington and West Virginia, have publicly criticized the agreement as insufficient. 

But prosecutors backing the agreement said they expect most states to greet the chance to have immediate funds to fight addiction.

"We want to get these monies in our communities as quickly as possible, and to the maximum amount possible because people are dying, and we want to save lives," said North Carolina Attorney General Josh Stein, who added that he expects more than 40 states to sign off on the deal. 

"We want to help people escape the prison of addiction so that they can be free and make choices about what they do every day, just like all of us do without having to be concerned about trying to find that morphine molecule to inject in their body."

Besides New York and North Carolina, the states that have already signed off are Connecticut, Delaware, Louisiana, Pennsylvania and Tennessee.

The settlement does not address cases currently being tried against Teva and Allergan, nor does it address the role of drugstore chains such as Walgreens and CVS that have also been sued. 

 Under the agreement, J&J agreed to pay up to $5 billion over nine years and to cease the sales of opioids nationwide, James said. 

The three distributors will pay up to $21 billion over 18 years and agreed to set up a centralized clearinghouse to help state officials track drug shipments and better guard against suspicious orders. 

The exact amount will be determined by overall participation of state and local governments, according to James' statement.