Severn Trent has confirmed that the four metres (13ft) wide and three metres (10ft) deep hole opened up in Stafford Street after one of its sewers collapsed and warned that repairs will be "very complicated" and take at least a month to complete.
The road outside Tyre City eventually collapsed on Thursday after gradually sinking in the days beforehand and the road is now closed.
A Severn Trent spokesman said: "Our teams have confirmed the issue was caused by a collapsed sewer under the road, which has now been closed to keep our teams and drivers safe.
"We’re out again this morning assessing the extent of the damage and working out how best to repair both the sewer and the road.
"At this early stage, it looks like it’s going to be a very complicated repair that’ll take at least four weeks to complete.
"We’d like to apologise to everyone who’s been affected by the closure and assure them we’ll be working seven days a week once we’ve got a repair plan in place to get everything back to normal as quickly as possible."
Aerial photos show the scale of the damage caused to the surface of Stafford Street at its junction with Proffitt Street.
Tyre City manager Sean Dickenson told the Express & Star how he had to run into the road to stop a Transit Van after seeing the ground was sinking on Thursday morning.
He explained: "We opened up on Monday and noticed there was a dip in the road. The cars were bouncing.
"Day by day it's been getting worse then this morning we were sitting here and could see the road sinking.
"Then the council came and put some signs up saying slow down.
"We were watching the road dip and all of a sudden a Transit van drown down and I had to run and stop it before the road caved in.
"He had to swerve on the pavement."
Walsall Council said they were made aware of a "shallow dip" in the road earlier in the week, which was inspected and as there was no visible cracking Severn Trent Water were advised and precautionary arrangements were made for a sewer investigation to be carried out.
Following inspection on Thursday, although there were no obvious signs of further deterioration, it was agreed that it would be necessary to close the road to facilitate Severn Trent’s investigation and signage was displayed to warn drivers of the uneven road surface, the authority added.
Councillor Adrian Andrew, deputy leader of the council said: “When it became apparent that we were dealing with more than just a routine highway defect, highway officers responded quickly, effectively and worked positively with West Midlands Police and Severn Trent to ensure the safety of the travelling public.
"Our priority now is to see the repairs completed as quickly as possible and Stafford Street reopened to traffic.”
Walsall Council said traffic is being diverted via Leamore Lane, Green Lane and Court Way and turnings from the Ring Road onto Stafford Street will be closed to northbound traffic.
Drivers have also been asked to avoid Hospital Street to reduce congestion.