A man has pleaded guilty to causing an explosion at a fast-food restaurant in Canberra last year by lighting a gas cylinder.

In September, Gyu Seon Park entered a McDonalds in Braddon and lit a cylinder that exploded, seriously injuring himself in the process.

When the incident happened, Park was on bail for a similar offence in which he allegedly went into a restaurant with petrol, but was prevented from igniting it after being wrestled to the ground.

After the explosion at Braddon, Park was charged with intentionally and unlawfully causing an explosion likely to endanger human life or cause grievous bodily harm.

He faced the same charge in relation to the earlier incident.

Park had originally pleaded not guilty to both charges by reason of mental impairment, but changed his plea to guilty today in the ACT Supreme Court.

Park was seriously injured in the Braddon explosion and taken to Concord Hospital in Sydney for treatment before being transferred back to the ACT where he was remanded in custody.

He did not apply for bail and will be sentenced in December.