Firefighters in Indonesia are struggling to contain a three-day-old fire at an illegal oil well that has killed at least three people and injured two others, a disaster relief official said on Tuesday.

Some 750 people have been evacuated from the densely populated areas around the site, located in Central Java province's Blora region, Agung Tri, a member of the provincial disaster mitigation agency's rapid response team, told Reuters.

The oil well was being operated without a permit by local residents when it caught fire on Sunday.

Authorities are still investigating the cause of the blaze, but residents living near the well said they heard an explosion before the fire broke out, Agung said.

The relief agency has deployed four excavators in an attempt to use soil to extinguish the fire, he added, but firefighters were still battling massive flames on Tuesday and facing difficulties moving equipment into the hilly terrain surrounding the site.

Evacuated residents have, meanwhile, been moved to temporary shelters and local government buildings nearby.

Local communities in the mineral-rich Indonesian archipelago have taken over hundreds of oil wells abandoned by companies after they proved to be no longer economically viable.

Many are illegally operated with lax safety standards.

Indonesian authorities have recently moved to legalise those operations, issuing a regulation in June that allows small companies to partner with residents. The policy is intended to boost the country's oil production while improving safety standards and protecting the welfare of communities.