Retail giant Amazon says it will build its own coronavirus testing lab to monitor the health of its staff.

Cases of Covid-19 have been reported at more than 50 Amazon facilities across the US. Some have involved multiple infected workers.

The company said it had assembled a team to build its own "incremental testing capacity".

Amazon staff have previously criticised the firm over its response to the coronavirus pandemic.

In March, Amazon fired a New York warehouse worker who organised a protest over a lack of safety precautions taken by the company.

Later, a memo from a meeting of Amazon executives was leaked. It said: "We should spend the first part of our response strongly laying out the case for why the organiser's conduct was immoral, unacceptable, arguably illegal, in detail, and only then follow with our usual talking points about worker safety."

'Regular testing'

Amazon blogged it had made more than 150 "significant process changes" in response to coronavirus.

"Our operations sites and grocery stores are distributing masks to employees and conducting employee temperature checks," the company said.

"A next step might be regular testing of all employees, including those showing no symptoms. Regular testing on a global scale across all industries would both help keep people safe and help get the economy back up and running."

The company acknowledged that testing resources were limited, so it had assembled a team of employees to develop its own facility.

"We have begun assembling the equipment we need to build our first lab and hope to start testing small numbers of our front line employees soon. We are not sure how far we will get in the relevant timeframe, but we think it's worth trying, and we stand ready to share anything we learn with others."

According to news site Bloomberg, at least one Amazon facility is being investigated by the US Occupational Safety and Health Administration over concerns it has not done enough to safeguard employees.

The Pennsylvania warehouse receives products from manufacturer before sending them to smaller Amazon warehouses around the US.