Image copyright AP Image caption The water restrictions affected over 300,000 people in the city of Corpus Christi

Residents of Corpus Christi, Texas, have been told it is safe to drink tap water again, after a chemical leak sparked a four-day ban.

The city's mayor said test results had showed no contamination, and locals could resume using water for drinking, bathing and cooking.

The ban was issued on Wednesday over fears that a leak at an asphalt plant could have tainted the water supply.

Long queues formed at grocery stores as shoppers stocked up on bottled water.

About 85% of Corpus Christi, which has a population of about 320,000, was under the restrictions.

Image copyright AP Image caption Shops saw a rush on bottled water during the four-day ban

The chemical behind the scare was Indulin AA-86, an asphalt emulsifier which can burn human skin in its concentrated form.

The leak took place at an asphalt plant leased to Ergon Asphalt and Emulsions by oil refiner Valero.

Mayor Dan McQueen told a news conference that investigations into the 24-gallon (91-litre) spill of Indulin AA-86 had determined that the water was safe to use.

It was not clear if the public water supply was ever contaminated by the chemical.

Image copyright Corpus Christi Caller-Times via AP Image caption Mayor Dan McQueen said test results showed no contamination

Officials said that none of the 28 drinking water samples analysed by the Environmental Protection Agency (EPA) tested positive for the contaminant.

However, the EPA said there have been seven "unconfirmed" reports of symptoms possibly related to prohibited water use.

Mr McQueen said officials would seek possible damages from those responsible for the leak.

There has been some confusion over exactly when city officials were notified of the problems at the plant that prompted the water use ban.

Image copyright AP Image caption Further tests will be carried out on Corpus Christi's water supply in the coming days

Valero Energy Corp said in a statement on Saturday that it had alerted the city to "milky, sudsy water" at the plant on 7 December - a full week before the ban was announced.

Ergon said the issue arose when "soap solution" flowed back into a pipe through which the plant receives water.

It said the pipe is not directly connected to the city's water main, but that the two are interconnected.

Corpus Christi locals have been warned to use water conservatively to avoid overtaxing the system.

The EPA will continue collecting and testing water samples in the city over the coming days.