South African authorities are concerned there could be a second explosion in Johannesburg's business district, after one person died and 48 were injured in a large blast on Wednesday.

Videos show a main road split wide open from the force of the explosion, with several vehicles blown onto their side.

It is still unclear what led to the blast, but officials suspect an underground gas pipe is responsible.

Officials have pleaded with the public to stay clear of the area.

The scene at Bree Street is still being treated as a potential risk area - emergency services remain there and people are being evacuated where necessary.

Several streets have been closed to traffic and electricity supply in the area has been sealed off, in what is usually one of the busiest parts of South Africa's commercial hub.

Officials from Gauteng province, which includes Johannesburg, suspect the blast may have been caused when some underground gas pipes ruptured.

Addressing the media on Thursday, Premier Panyaza Lesufi said 12 people are still being treated in hospital for their injuries.

A preliminary inquiry did not establish the cause of the blast and investigations are underway to determine what happened, he told reporters.

Local supplier Egoli Gas said on Thursday that they had found a small leak in one of their pipes, but they believe it is unlikely that it led to the explosion.

The firm has been asked by authorities to check on their other pipes in the area, as a possible gas leak still the focus of investigations.

On Wednesday evening, witnesses reported feeling the ground shake then hearing a loud bang moments before the earth opened, and a section of Bree Street collapsed.