Beijing (AFP) - A fresh explosion rocked a Chinese town Thursday, a day after 17 parcel bombs killed at least seven people and wounded scores more, state media reported.

No injuries were reported in the latest blast, which came hours after apartment buildings were brought down and a supermarket was shattered in a wave of bombings in southwest Guangxi.

Police were quick to rule out a "terrorist act", saying on Wednesday they were treating the explosions as a "criminal case". The apparent attacks come amid a wave of unrest linked to China's Uighur ethnic minority.

The six-storey residential building hit Thursday sustained "some damage", media reports said.

Pictures showed bricks scattered around the site, which authorities had sealed off.

China National Radio's blog site CRI quoted a resident who said he was shaken awake by the blast and "thought there was an earthquake".

At least 13 places were hit on Wednesday, including a prison, a government office, a train station, a hospital and a shopping centre.

Pictures showed one six-storey building gutted and collapsed, and streets littered with glass, bricks and other debris.

Other photos posted online, which could not be verified, showed overturned cars, victims bandaged and laid on makeshift stretchers and plumes of grey smoke rising above a residential district.

The explosives were apparently placed in express delivery packages, the official Xinhua news agency said.

Police said late Wednesday that 51 people were injured and two people remained missing.

Local media reported that post offices in the area had beefed up security measures and halted package delivery until October 3.

On China's Twitter equivalent, Sina Weibo, police urged the public not to accept material from strangers and warned residents not to take packages from "unofficial channels", Xinhua said.

A 33-year-old local man had been arrested, authorities said, providing no immediate explanation regarding a possible motive.

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Xinhua reported Thursday that police were looking into whether the suspect, named as M. Wei, "hired others to help deliver letter bombs".

The explosions took place on the eve of the national day holiday, during which some government offices and companies take the week off.

Disgruntled Chinese citizens have in the past bombed local government offices and public places to try to draw attention to their grievances.

In 2013 a man set off a series of home-made bombs packed with ball bearings outside a provincial government headquarters in northern China, killing at least one person and wounding eight.

Xinhua said at the time he sought to "take revenge on society".

But several Chinese cities have been hit in recent years with explosions that the police have blamed on Uighurs, a mostly-Muslim minority from the far-west Xinjiang province.

That included a fiery vehicle crash in Tiananmen Square, Beijing's symbolic heart, in 2013 in which three members of the same Xinjiang family killed two people before setting their own car on fire.

Rights groups accuse Beijing of cultural and religious repression which they say fuels unrest in the region bordering Central Asia.