Lego has opened a US$1 billion factory in Vietnam that it says will make toys without adding planet-warming gas to the atmosphere by relying entirely on clean energy.

The factory, which opened on Wednesday in an industrial area close to Ho Chi Minh City, is the first in Vietnam that aims to run entirely on clean energy. Lego says it will do that by early 2026.

It's the Danish company's sixth worldwide and its second in Asia. It will use high-tech equipment to produce colourful Lego bricks for Southeast Asia’s growing markets.

“We just want to make sure that the planet that the children inherit when they grow up needs to be a planet that is still there,” Lego CEO Niels Christiansen said.

The factory is an important factor in Lego's quest to stop adding greenhouse gases by 2050. It has a shorter-term target of reducing emissions by 37 percent by 2032.

The privately-held group, which currently makes its bricks out of oil-based plastic, says it has invested more than US$1.2 billion in a search for more sustainable alternatives. But those efforts have not always been successful.

Vietnam also aims to achieve net-zero emissions by 2050, so it needs more of its factories to use clean energy.

The country hopes the plant’s 12,400 solar panels and energy storage system will help set a precedent for more sustainable manufacturing. (AP)