Some 18,000 people were evacuated from a Chinese coastal city after an oil pipeline explosion killed at least 47 people and sent thick black smoke billowing into the sky, a local government report said Saturday.

The Friday morning blast in Qingdao ripped roads apart, pictures showed, while leaving many sections of the city cut off from utilities.

The latest government report Saturday did not explicitly state a reason for the evacuation, mention its timing, or whether people had been able to return to their homes.

But, according to official media, students from nearby schools and local residents were handed out masks over fears of possible toxic emissions.

The Global Times later reported: "Environmental monitoring shows that the concentration of toxic materials is within national standards".

The impact of the blast disrupted the supply of water, gas and electricity in parts of the city, with the government distributing 2,000 candles on Friday night.

Authorities also provided 40,000 servings of free food for breakfast and lunch on Saturday.

Electricity has now been restored in all but two communities in the district, the local government said.

The pipeline, run by state-owned oil giant Sinopec, sprang a leak early Friday and exploded several hours later as workers sought to repair it, the Qingdao municipal government said in its verified account on Sina Weibo, a Chinese equivalent of Twitter.

Sinopec chairman Fu Chengyu told state television on Saturday: "(We) are deeply grieved, we express our deep condolences for the dead, our support to their families ... and our apologies to the whole country.

"(We will) find out the accident's causes as soon as possible and give a reasonable explanation to everyone."

Sinopec said that the pipeline, which was put into service in 1986, was 248 kilometres (154 miles) long and carried some 10 million tonnes of oil per year.

Authorities on Saturday also turned their efforts to containing the oil spill as it spread out into the sea over an area covering 3,000 square metres.

Oil booms and 22 clean-up ships were deployed in the zone, tasked with spraying 10 tonnes of oil dispersants, reported the Xinhua news agency quoting local officials.

China has a very poor record on industrial safety as lax law enforcement and corruption enables business owners to cut corners or offer bribes to evade standards.

Around 28,000 people were killed or went missing in workplace accidents in the first half of this year, state media have reported.