Police were forced to draw their guns when Glen Maxwell Colefax charged at them while holding the improvised incendiary device in January.

Colefax, 33, was originally charged with eight offences over the incident, including lighting a fire outside during a total fire ban, using an offensive weapon, and traffic offences.

He pleaded guilty in the ACT Supreme Court on Wednesday to threatening to cause harm to a public official.

It is understood the other counts have either been dropped or will be scheduled.

Court documents said Colefax gave police the finger while driving along Belconnen Way about 7.25pm on January 17.

He then swerved erratically, crossed two lanes, and performed an illegal U-turn.

Police gave chase and Colefax continued to give them the finger as he fled.

The offender continued to drive in both lanes of traffic, and narrowly missed several cars when he turned onto Eastern Valley Way.

The chase ended when Colefax was cornered in a cul-de-sac.

The offender then swore at police and moved towards them while shaking containers – which contained brake fluid and chlorine - he had in his hands.

The containers let off blue smoke and Colefax prepared to throw them at police.

But he instead fled on foot after police drew their guns and told to him to stop.

He discarded the containers which ignited, forcing police to stop the chase and use extinguishers to put out the fire.

Colefax was arrested soon after and taken to Calvary Hospital suffering burns to his foot caused by the chemical cocktail seeping into his shoe.

He later told police he expected to be arrested for "pathetic [unrelated] breaches" so decided to commit the offences because "if I'm going to come here I may as well come here for … something for real".

Colefax also admitted he had been on ice at the time of the offence.

The matter was listed for sentence in February.