A bipartisan group of United States senators is reported to have made substantial progress towards achieving a deal to overhaul the US immigration system.

Charles Schumer, a Democrat and key member of the so-called Gang of Eight, made up of four Democrats and four Republicans, said "every major policy issue has been resolved".

However, Republican Senator Marco Rubio said while progress had been made, reports that the group have agreed on a legislative proposal are premature.

Efforts are continuing to draft legislation that would include a pathway to US citizenship for an estimated 11 million undocumented immigrants.

The legislation is also intended to improve border security and secure agreements on pay for low-skilled workers, while providing protections for American employees.