Drums of "extremely toxic" chemical waste have been dumped in bushland near a popular Melbourne walking track, requiring complex and lengthy clean-up operations.

Authorities were first made aware of dumped chemicals on Wednesday morning last week when they found nine drums rolled down a gully just off Mount Dandenong Tourist Road near Upper Ferntree Gully.

Nine drums of chemical waste were found dumped just off Mount Dandenong Tourist Road. Credit:Upper Ferntree Gully CFA/Facebook

The chemical drums were found near the 1000 Steps, the popular three-kilometre Kokoda Track memorial walk. Five of those drums were empty.

A Facebook post from the Upper Ferntree Gully CFA crew said it quickly became apparent when they found the drums that they were likely to contain "extremely toxic substances".