BEIJING, JAN. 4 -- Foreign students demonstrated today against alleged mistreatment by Chinese police of a Mexican student after unknown assailants pushed him off a hotel roof last week, seriously injuring his back.

Francisco Reyes, 33, an art student from Mexico City, said from his hospital bed here that police detained him for seven hours, denying him emergency medical treatment.

Reyes said he may have lost the use of his legs for years and possibly for life.

Mexican Embassy counselor Benjamin Wong quoted doctors as saying Reyes was semiparalyzed because of spine damage. The embassy has asked the Chinese authorities for an investigation and explanation of the incident, Wong said.

Angry foreign students gathered in central Beijing today and marched to the Ministry of Public Security, which controls China's police, to demand an investigation. Witnesses said police confronted the 50 students and blocked the entrance to the ministry.

Reyes said that on the night of Dec. 30 he went with three Chinese friends to a hotel and drank with them in a room. His friends left, and a Chinese stranger came in, tried to pick a fight and accused the student of being a spy, Reyes said.

The student said he tried to leave the hotel but was stopped by staff. In desperation, he said, he went out onto a roof, but men with flashlights pursued him and pushed him off. He fell around 12 feet, injuring his back, he said, and his assailants returned and kicked him on the ground.

During his police detention, Reyes said he was immobile because of his back injury but police did not believe him.

After agreeing to let him go to the hospital, policemen dumped him in the street although he could not walk, he said. After he shouted in protest they called a taxi for him, Reyes said.