A teenager who led police on a car chase "panicked", a court has heard.

Matthew Alexander Reid Smith was driving in breach of his restricted licence in the early hours of December 27 when police tried to pull him over.

He was driving in a 50km/h section of urban road, but was speeding when police tried to catch up with him, police prosecutor Sergeant David Grey said.

Smith initially slowed when police activated the patrol car's lights, but then accelerated away. He then took police on a chase, at one point reaching speeds of 105km/h.

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During the chase, Smith had to brake hard, causing his wheels to lock and his car to skid across the opposite lane and on to a grass verge, Mr Grey said.

When he eventually stopped, a breath test showed him to have 392mcg of alcohol in his system. Under-20 year olds are not allowed to drive after drinking any alcohol.

Smith told police: "I panicked. I accelerated when I should have braked."

He pleaded guilty in the Whanganui District Court on Tuesday to dangerous driving, failing to stop for red and blue flashing lights, and having alcohol in his system while being a person aged under 20.

Smith had no criminal history.

Defence lawyer Harete Hipango said Smith told her he did not realise it was a police car behind and thought he was being tailgated, and panicked.

"He stands in the dock with his head bowed, sir. He's aware that he has done wrong," she said.

Ms Hipango said Smith not only had to face the "wrath of the court", but also that of his family.

Judge David Cameron said he was not sure about "this business of not knowing who it was".

"He slowed down, for goodness' sake, and only accelerated when the police lights came on."

He described the offending as "all in all, disgraceful behaviour".

Judge Cameron fined Smith $950, $130 court costs, and disqualified him from driving for nine months.