Image copyright AFP Image caption A protester uses a torch light while crawling within a sewer tunnel to see how wide it is

Some of the last protesters remaining at a besieged university in Hong Kong have tried to escape and evade police by crawling through sewers.

Hundreds of protesters have already left PolyU but dozens remain inside.

The campus - the scene of some of the most intense clashes witnessed during months of anti-government protests - is surrounded by police who are arresting for rioting any adults trying to leave.

Six people were arrested on Wednesday for an attempted escape via the sewers.

The group included two men climbing out of an underground drain and four people - three men and a woman - who had removed a manhole cover and lowered a rope into the drain to assist them, police said.

"It was complicated and dark down there, I wanted to get home as soon as possible," one young man who unsuccessfully attempted a sewer escape told BBC Chinese. "But how else could we leave the PolyU campus?"

The four-day campus siege at PolyU - Hong Kong Polytechnic University - has been one of the most dramatic confrontations in the wider protest movement that has paralysed the city for more than five months

The protests started after the government planned to pass a bill that would allow suspects to be extradited to mainland China. The bill was eventually withdrawn, but the demonstrations continued, having evolved into a broader protest against alleged police brutality, and the way the former British colony is administered by Beijing.

PolyU is the last of five Hong Kong universities that protesters had occupied in the last 10 days. Fewer than 100 hardcore demonstrators remain on the campus after days of violent clashes with security forces.

Many have surrendered to police or emerged as part of medical evacuations. More than 1,000 people have been arrested. Those under 18 were allowed to go home but had their details registered.

Image copyright Getty Images Image caption Fire service divers searched the tunnels for any trapped protesters

Several small groups of protesters seeking to avoid possibly years in prison if arrested on rioting charges have reportedly attempted a dangerous escape route through the sewers. They have descended into the tunnels armed with torches and gas masks.

The fire brigade have now blocked the main entrance into the sewers within the PolyU campus to thwart such escapes. On Tuesday and Wednesday divers searched the tunnels for any protesters who might have been trapped but found none.

Whether any protesters have successfully escaped via the sewers remains unclear, despite rumours on campus to the contrary. The two arrested on Wednesday made it about half a kilometre from the university when they emerged and were arrested.

Bowie, a 21-year-old student who made an attempt, told Reuters news agency: "The sewer was very smelly, with many cockroaches, many snakes. Every step was very, very painful. I'd never thought that one day I would need to hide in a sewer or escape through sewers to survive."

Image copyright Getty Images Image caption One protester makes a daring escape

Her group spent an hour swimming in the fetid water, but when they emerged, were crushed to realise they were still within the university grounds, she said.

Tunnelling out of campus is just the latest escape plan hatched by increasingly desperate protesters. On Monday, dozens slid down ropes from a bridge, fleeing on waiting motorcycles. Police said nearly 40 of them were later arrested.

Some have tried to flee under cover of darkness while many others have tried to get through police lines, some being beaten before being arrested.