(Bloomberg) -- Climate campaigner Greta Thunberg was accused of breaking public protest laws on the first day of a London trial after she was arrested while blockading an oil and gas conference last year.

The Swedish activist, 21-years-old, arrived at Westminster Magistrates Court on Thursday to stand trial with four other protesters. Thunberg, who pleaded not guilty, was arrested on Oct. 17 during a protest at Energy Intelligence Forum at the Intercontinental Hotel where oil and gas executives were speaking. 

Prosecution lawyers described how a large number of protesters blocked entrances and exits of the hotel from 7am. Police imposed a public order act, which means they had to stay in a designated area or face arrest, after protesters refused to stop blocking the hotel’s entry points.

The arrest highlights how policing of protests has hardened since the Conservative Government pushed through new laws in May after a spate of environmental protests caused disruption to critical infrastructure around the country. Thunberg and the others face a fine if they are found guilty.

The protesters slowly grew in number from around 50 to 200 with conference delegates and hotel guests unable to get in or out of the hotel, senior police officer Matthew Cox said giving evidence. 

He said there was a large number of drummers, people letting off multiple smoke flares, and protesters trying to get into the hotel forecourt. Police resources were depleted and they tried to move the protesters before they issued the order, not taking the decision lightly, he said.

Dozens of supporters gathered outside the court on Thursday morning, holding signs that read “climate protest is not a crime.” Thunberg, who is yet to speak in court, took notes throughout the hearing.

Read More: Thunberg Charged by Police Over London Oil Event Protest

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