Washington state is on the verge of becoming the first in the US to allow humans to be turned into compost, amid a surge in demand for sustainable and 'positive' funeral services.

State representative put the final touches to a bill on Friday which legalises two sustainable death care options - a chemical process of alkaline hydrolysis and a natural process of organic reduction.

The bill has now arrived on the desk of Washington's governor and 2020 Democratic presidential candidate, Jay Inslee, who is expected to sign it into law within days.

The 68-year-old announced his bid for the presidency last month, highlighting his pro-environmental record as governor as he pitched himself as the only candidate committed to making tackling climate change their first priority in office.

Proponents of the human composting bill say an environmentally friendly after-death service is badly needed with an ageing population and as an alternative to costly burial services.