NYT, BEIJING—A fire that tore through a karaoke bar in southern China in the early hours of Tuesday killed 18 people, the police said, adding that arson was probably the cause.

A brief initial police account of the blaze in Qingyuan, a city in Guangdong province, said firefighters received an emergency call about 30 minutes past midnight.

By the time they extinguished the fire about 25 minutes later, the karaoke bar was gutted. In addition to the 18 dead, the police said, five people rescued from the fire were hospitalized.

“According to a preliminary investigation, the blaze was arson,” the online statement from the Qingyuan police said. “Currently, the public security authorities are stepping up their investigation.”

Video footage shown by Chinese news outlets showed bystanders watching helplessly as intense flames flared out of the three-story building containing the karaoke bar and climbed up its walls.

The police did not identify a suspect or motive, nor did they say how many of the dead were found in the bar. Often karaoke bars in China feature small rooms padded with carpet, and at least some of the dead may have been trapped in such rooms.

The person believed to have started the fire had been in a quarrel beforehand and used a motorbike to block the only entrance to the karaoke club, then lit the fire at the door, a reporter for CCTV, the state-run broadcaster, said in an online report that did not cite the source of the account.

The China News Service, a state-run news agency, said police in Qingyuan — an industrial and commercial center — had blocked off roads to catch the person responsible.

The deadly fire is likely to prompt another round of calls from the Chinese government to tighten up safety, especially in the crowded fringes of cities and industrial zones where fires often break out.

After a fire roared through an apartment on the outskirts of Beijing in November, killing 19 people, the city intensified a program to expel migrant workers who live in such areas, displacing hundreds of thousands of people.