As police encircled the Polytechnic University in Hong Kong last weekend, trapped and fearful students began desperately cooking up ways to escape.

Key points: One of the students told the ABC many inside the university feared they would spend their futures in jail

One of the students told the ABC many inside the university feared they would spend their futures in jail He described the event as a "unforgettable experience" for the young people of Hong Kong

He described the event as a "unforgettable experience" for the young people of Hong Kong He did not specifically say how he escaped to avoid tipping off police

It began with great optimism — a group of hundreds ready to defend themselves and become the symbol of Hong Kong's democratic movement.

The daring escapes — and attempts — included crawling through sewer systems, sliding down plastic hoses to a road where waiting scooters raced in to pick them up and other secret methods.

Seventeen-year-old high school student Simon*, who escaped on Monday afternoon, won't say exactly how he got out for fear of tipping off police.

He escaped with around 10 others but believes officers now know how he got out.

He told the ABC being barricaded inside was "scary", but an "unforgettable moment".

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 42 seconds 42 s Students rappel from bridge to escape police

At the beginning he said many inside were enthusiastic and optimistic, ready to defend themselves and become the symbol of Hong Kong's democratic movement.

"This is not the Hong Kong that I want to be in," he said.

"I want to change — even just an ordinary citizen.

"If thousands of us can come out and do it, generate a power that can't be [ignored], then we will have some influence in society — even if we are young."

Students try to extinguish a fire at the entrance of Hong Kong Polytechnic University. ( AFP: Ye Aung Thu )

But as police sealed the exits and surrounded the campus on Sunday, the mood inside began to shift.

When some tried to leave using the main exit, they were pushed back — met with tear gas and water cannons.

"I still remember the atmosphere — it was very desperate," he told the ABC.

"At that time people were getting exhausted because they had had many hours without rest … so many people were exhausted and they started to be pessimistic because they thought they may not be able to defend themselves.

"Many people were crying — they feared they would spend their future lives in jail."

Many protesters tried to escape via a sewage tunnel inside the Hong Kong Polytechnic University campus. ( Reuters: Adnan Abidi )

One thing he didn't see was any regret.

"No-one regretted their decision to come to Poly U," he said.

"It was the most unforgettable experience for the youngsters of Hong Kong".

As word began that there were hundreds trapped inside, surrounded by police, protesters came out in huge numbers trying to swarm the campus.

Running battles broke out surrounding the campus — a human Molotov cocktail production line brought supplies to the frontlines on Monday night.

It was all about trying to distract the officers — but protesters were outnumbered.

Hong Kong protesters crowdsourced the production of Molotov cocktails. ( ABC News: Jake Sturmer )

The reason Simon was so desperate to escape? To get back to school.

"Although protests are a way to change society, studying is also another way," he said.

"If I manage to get a good result, get into university, get a good degree, then I can maybe do something to change the society, change the government too."

One thousand people have been arrested since Monday and hundreds of minors were photographed and had their details recorded by police.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 42 seconds 42 s PolyU students prepare themselves for riot police as they attempt to break out of the university

Adults arrested face up to 10 years jail and police say they have reserved the right to investigate those under 18 later.

There are still some desperate holdouts inside the campus, and Hong Kong police on Saturday said that "a peaceful resolution was always their aim to solve the ongoing conflicts."

"Police appeal to all staying in the campus to leave in a peaceful manner and pledge to bring offenders to justice in a fair manner," the Hong Kong Police Force stated in a tweet.

Police detained protesters after they tried to escape the campus of the university the Hung Hom district of Hong Kong. ( AFP: Anthony Wallace )

For Simon, it's been a scary time — but he says "nothing is more scary than losing Hong Kong to China".

*Name changed to protect identity.