These tours are on a booking website and cost between S$63 and S$300 per person.

The universities said they did not make these listings.

NTU said these tour operators are not part of their official tour program.

NTU does not see its campus as a tourist place and does not work with tour operators.

Only official NTU tours are allowed, and the school is looking into these unauthorized listings.

NUS said it does not work with or approve any outside tour operators.

NUS warned people about unauthorized tours on its social media on August 1.

This warning was posted at the start of the summer travel season.

The warning said unauthorized guided tours are not allowed and will be stopped.

It told people to make sure tours are approved by the university before booking.

CNA joined an unauthorized tour at NTU to see what happens.

The tour cost S$154 and showed people around the campus.

The group saw many places, including a lecture hall and residential halls.

The guide tried to get into some rooms, but they were locked.

Some areas, like the library, could only be seen from outside.

The guide was a PhD student from China and not an official tour guide.

He was introduced to the job by a senior student and has been doing it for a month.

He earns more than official student guides, who get paid by the school.

The PhD student does not know how the tour arrangement started.

He said many students do this kind of work to earn extra money.

He also said the unofficial tours fill a gap since NTU does not offer daily tours.

The student said it helps him pay for rent and is convenient.

NUS said only licensed student guides can give tours on campus.

Students who give unauthorized tours can face disciplinary action.

Licensed guides from the Singapore Tourism Board can also give tours on campus.

NTU said travel agencies need approval before giving campus tours.

CNA contacted the two tour operators selling unauthorized tours.

One operator did not answer questions about its connection to the universities.

The other operator said it started the campus tours last summer.

It said NUS and NTU are popular destinations for Asian families.

The operator gets around 100 to 200 participants a month, mostly from Asia.

It listed on the booking website to reach more customers.

The operator said its guides are trained student representatives.

The operator did not answer questions about its connection to the universities.

It said many parents want their children to experience the campus atmosphere.