Melbourne's safe injecting room will be expanded amid growing demand from drug users in the inner-city overdose hotspot.

Melbourne's new safe injecting room is set to be expanded just months after opening in an inner-city overdose hotspot.

About 8000 people have used the supervised injecting room at the North Richmond Community Health Centre since late June and staff have responded to 140 overdoses, the government says.

Construction on a purpose-built $4.9 million publicly-funded facility in the centre's car park is due to begin in September.

The new building aims to keep up with high demand for the injecting room and boost treatment and counselling provided.

"Two months in, the medically-supervised injecting room is doing exactly what we hoped. It's saving lives," Minister for Housing, Disability and Ageing, Martin Foley, told reporters on Friday.

Without the centre, the minister said people would have overdosed "in alleyways, in car parks, in the schoolyard and suffered terrible, lonely trauma as a result, and sadly too many deaths".

Its medical director, Dr Nico Clark, said drug users were "very happy" with the service.

"They feel like it's a safe place for them to come, a place where they can have a positive interaction with health staff and where when can not only use the drugs they're using in a safe way but also find access to other treatment," he said.

The injecting room is modelled on Sydney's Kings Cross centre. It is due to be reviewed in 2020 and possibly extended for another year.