Families of Boeing 737 MAX crash victims on Wednesday asked US authorities to impose a fine of up to $24.8 billion on the aviation giant and proceed with criminal prosecution.

The move comes a day after Boeing CEO Dave Calhoun acknowledged the "gravity" of the company's safety problems and assured a US congressional panel that it was making progress on the issue.

Sitting behind him in the audience were relatives of victims of the Boeing 737 MAX 8 crashes in 2018 and 2019, who held up victims' photos.

"Because Boeing's crime is the deadliest corporate crime in US history, a maximum fine of more than $24 billion is legally justified and clearly appropriate," Paul Cassell, a lawyer for the families, wrote in a letter to the US Department of Justice.

The 32-page document explains the calculations behind the amount sought, saying Boeing "should be fined the maximum -- $24,780,000,000 -- with perhaps $14,000,000,000 to $22,000,0000,000 of the fine suspended on the condition that Boeing devote those suspended funds to an independent corporate monitor and related improvements in compliance and safety programs as identified below."

It added: "And Boeing's Board of Directors should be ordered to meet with the families."

The families also believe the government should promptly "launch criminal prosecutions of the responsible corporate officials at Boeing at the time of the two crashes."

The case relates to crashes in 2018 and 2019 in Indonesia and Ethiopia that together claimed 346 lives and comes as Boeing faces intensifying scrutiny following recent manufacturing and safety problems.

The aviation giant has again been in the public spotlight since a January 5 incident in which a 737 MAX operated by Alaska Airlines was forced to make an emergency landing after a fuselage panel blew out mid-flight.