* Fewer than 100 protesters still on campus -witnesses
* US Senate approves Hong Kong legislation
* China condemns US 'interference', Hong Kong expresses regret
* Protesters search sewer system for a way out
* New police commissioner makes late-night visit to scene
The last band of anti-government protesters trapped inside a besieged Hong Kong university were weighing a narrowing range of options on Wednesday, with some trying to escape through sewers, as police outside appeared ready to simply wait them out.
Reuters witnesses said fewer than 100 protesters remained inside the Hong Kong Polytechnic University after more than 1,000 were arrested since late on Monday.
Some surrendered, while others were nabbed in escape attempts that included trying to clamber down ropes onto waiting motorbikes. Some protesters resurfaced inside the campus after unsuccessfully probing the sewers for a way out during the night. It was unclear if any had managed to escape that way.
A fire services diver was seen entering and emerging from a campus sewer opening during the night.
"It has been a disastrous life for us spending these days in Polytechnic University, because we can't live here. The supply of food, water, electricity is going to be run out," said a student named Alesa, who said she had tried twice to escape through the sewer.
"It's in vain," she said. "I'm a bit upset, but overall, I'm peaceful. I think if a generation are destined to be criminals, who is to save the next generation?" she said.
Police searched for potential escapees during the night with spotlights rather than using the tear gas and rubber bullets that had marked clashes in recent days, heeding calls from Hong Kong leader Carrie Lam for a humane end to a siege that saw the most intense clashes since the protests escalated more than five months ago.
They also tightened barricades in the streets surrounding the university, making them secure enough to be visited late on Tuesday night by the force's new commissioner, Chris Tang, at the end of his first day on the job.
Tang earlier urged the support of all citizens to end the unrest triggered by fears that China's central government is stifling the former British colony's freedoms and extensive autonomy guaranteed in its handover to Chinese rule in 1997.
Tang is under pressure to restore police morale as well as public confidence in a force that has come in for widespread criticism for increasingly violent tactics to suppress the protests. Police deny accusations of using excessive force.
The police quietly rolled out a new, harder-edged motto on Tang's first day, replacing "We Serve with Pride and Care" with "Serving Hong Kong with Honour, Duty and Loyalty".
Police have made more than 5,000 arrests since citywide protests escalated in June.
Chinese leaders say they are committed to the "one country, two systems" formula put in place in 1997 and have accused foreign countries, including Britain and the United States, of stirring up trouble.
In Washington, the US Senate unanimously passed the "Hong Kong Human Rights and Democracy Act", which would require the secretary of state to certify at least once a year that Hong Kong retains enough autonomy to qualify for special US trading consideration and would impose sanctions against officials responsible for human rights violations.
The bill must be reconciled with similar legislation approved by the House of Representatives. Senate aides said they expected it to move forward eventually as an amendment to a massive defence bill expected to pass Congress later this year.
China's foreign ministry condemned the passage of the bill, saying the United States should stop interfering in Hong Kong and Chinese affairs and move to stop the latest bills on Hong Kong from becoming law.
The Hong Kong government expressed "deep regret" over the bill's passage.
The unrest marks the most serious popular challenge to Chinese President Xi Jinping since he came to power in 2012.
Some protesters emerged as the sun rose above the Hong Kong Polytechnic University campus after a night spent sleeping on yoga mats to express a range of feelings, from defiance to uncertainty.
Others considered hiding in the maze of campus buildings, as they said a teacher had advised them to do.
"I already know where I will hide," a 19-year-old student, who gave his name only as Paul, said as he emerged in a hoodie, shorts and slippers to ask about breakfast in the canteen.
"I have enough food for at least a week and then will see what happens," he said.
Two protesters in full body armour, wielding metal rods, were going to get some sleep in the library after their night shift watching police movements outside.
"We need some energy to get ready for the big fight. Now that there's not many of us left they may want to come in," said a former student named Marc, 26.
"We know this place, it's our home and it is a maze. And we have weapons. We're not going to give up now, it's too late for that," he said.
Protesters still have stocks of petrol bombs, bows and arrows and other makeshift weapons after a weekend of fiery clashes.
One protester practised firing arrows at a campus tower shortly after dawn.
The university on the Kowloon peninsula is the last of five that protesters had occupied to use as bases from which to disrupt the city over the past 10 days, blocking the central Cross-Harbour Tunnel outside and other arteries.
"It's still incredible we defended it for such a long time," said Ricky, a 21-year-old student. "Since the police have taken control, many started to feel afraid and left and now many of us feel desperate and unhappy because we lost some support."