* First acknowledgement that protesters were hurt in China's south
* City official apologises, dismisses "exaggerated" reports
* Demonstrations spread to other towns (Recasts with comments from Maoming government, updates throughout)
By Megha Rajagopalan
BEIJING, April 3 (Reuters) - Officials in a southern Chinese city acknowledged on Thursday that 15 people were hurt "accidentally" at a mass protest against a chemical plant, days after police made no mention of injuries in a case that has incensed many Chinese.
But the deputy police chief of Maoming also denounced as "pure rubbish" news and online acounts of the upheaval last Sunday that said several people had died. Reports of the unrest had sparked demonstrations in nearby towns by sympathisers.
"In the course of cleaning up the scene, because the gathering of people was complicated...and at its peak with 1,000 people, on-duty police officers may have accidentally injured some of the bystanders," deputy chief of public security Zhou Peizhou said, according to a report by the city's news site.
"In this, I represent public security organs in offering sincere apologies."
Officials said 15 people were injured, including four police officers.
Protesters told Reuters they had seen several people killed in the protest and dozens injured.
The People's Daily, the ruling Communist Party's official newspaper, had earlier dismissed as false reports that police had killed 15 people and injured more than 300. It said two people were injured during the demonstration on Sunday.
In his comments on the city's news website, Zhou said the only death in the area had been that of a person killed in a motorcycle accident before dawn on Monday.
"Those who are exaggerating this by saying that police killed people are just spreading pure rubbish," Zhou said.
Police, he said, had detained 18 people on suspicion of causing public disturbances and provoking disputes. He said protesters had overturned and smashed a government vehicle and hurled stones and glass bottles at storefronts.
Unverified photos circulating on Chinese social media early this week, later deleted by censors, showed demonstrators lying in pools of blood and ambulances taking away the injured.
An unverifiable video of Sunday's protest, obtained by Reuters, showed police in riot gear chasing protesters, wielding batons and firing tear gas. Images of the protests sparked a public outcry.
A smaller protest took place on Thursday in the nearby city of Shenzhen, an organiser told Reuters by telephone, but participants were whisked away in police cars. They were questioned at a police station for several hours before being released.
"I don't know how long demonstrations can continue when police are clamping down so quickly - it's gotten much more difficult," said the protester, surnamed Xi. "Even those who simply post pictures online are now facing pressure."
The demonstrations spread to the provincial capital of Guangzhou on Tuesday, where police detained eight demonstrators, but they were released by Wednesday evening, sources with direct knowledge of the matter said.
One of those detained, reached by telephone, said none had been charged with any crime.
"We never had any physical conflict with the police," she said. "There was really no reason to charge us with any crime."
They were held for 24 hours at a police station, she said, adding that she regretted joining the demonstration and believed she had been misled by violent images online.
The People's Daily said some photos posted online were not of the demonstration, but old news photos of a domestic spat.
The protests are over a proposed plant to produce paraxylene, a petrochemical used in making plastic bottles and fabrics. It will be owned jointly by CNPC and Maoming's local government. (Additional reporting by Donny Kwok in Hong Kong; Editing by Michael Perry and Ron Popeski)