Chengdu Metro has apologized after an employee refused to allow a blind person's guide dog to enter a subway station on Tuesday.

When Chen Yan, a blind piano tuner from Beijing, tried to take the subway at Tonghuimen station in Chengdu, Sichuan province, an employee asked her for the birth, adoption and domestication certificates for her dog. As she had none of the documents, Chen had to leave.

She posted details of the incident on her mircro blog on Tuesday evening, but Internet users were puzzled because Chengdu Metro said in August it would allow blind people to travel with guide dogs.

Less than three hours later, the company said on its micro blog that the employee was unaware that guide dogs could accompany the blind on the subway, because it was the first time she had seen a guide dog in a subway station.

While apologizing and welcoming guide dogs on the subway, the company said the policy of asking for the three certificates was in line with regulations made in other cities with subways, the news portal scol.com.cn reported.