Image copyright AP Image caption Water bans remain in place for most city residents

Corpus Christi officials have identified a chemical that is suspected to have leaked into the Texan city's tap water on Wednesday night.

The contaminant, they say, is Indulin AA-86, an asphalt emulsifier which can burn human skin in concentrated form.

On Wednesday the city of 320,000 people announced that residents should not touch, drink or use the water.

The ban has since been lifted for some city dwellers while officials investigate the origin of the spill.

After a night-time meeting of the city council on Thursday, officials released a map of the city, showing that residents in the outlying regions could resume using city tap water.

Angry residents had gathered outside city hall throughout the day to call for answers and to chant "What do we want? Clean water! When do we want it? Now!".

As of Friday morning, about 15% of city residents were told they could use their water.

Corpus Christi residents warned not to touch tap water

Image copyright City of Corpus Christi Image caption People living in the blue parts of the map have been told they can use water from the tap

Image copyright AP Image caption Shoppers have stood in long lines to stock up on drinking water

State officials have pledged to help the city, with the Texas Division of Emergency Management sending shipments of bottled water to the state.

A run on grocery stores had emptied shelves immediately after the ban was announced.

Water bottle distribution centres have been set up across Corpus Christi to establish the more than 100,000 cases that have been donated from around the country.

FedEx has said they will disrupt some holiday shipments in order to ensure the delivery of bottled water to the Gulf of Mexico city.

Officials say that about three to 24 gallons of the petroleum-based, glue-like substance was released by Ergon Asphalt and Emulsion Inc after a "back-flow incident" in the city's industrial district.

Official say no reports of illness or injury has been reported related to the recent contamination.

Image copyright AP Image caption School Superintendent Dr Arturo Almendarez displays water for his students

Image copyright AP Image caption School worker Leeroy Luna moves crates of water into the Magee Elementary School.

The Mississippi-based company has not taken responsibility for the spill and in a statement said it had been in contact with the Texas Commission on Environmental Quality and had been "working cooperatively to provide all information to ensure state officials can remedy the situation as quickly as possible."

City spokeswoman Kim Womack told a local news station that officials had inspected the suspected site of the contamination and had not found a "backflow preventer".

"They're saying there is one and we're telling them 'show us,'" she told KRIS-TV.

"In the simplest terms, someone was careless when they were injecting chemicals with a pump and ... when the injection occurred, it crossed over into our water system."

Corpus Christi has struggled with water issues frequently in the past few years.

In May, Corpus Christi officials issued their third boil-water advisory in a year, which instructs residents to boil all water before using it.

Officials said at the time that heavy rainfall had caused elevated levels of nitrogen-rich runoff in the water supply.

In 2015 water-boils were issued due to elevated levels of E coli bacteria and another time for low levels of chlorine.