Chinese ventilators that ministers heralded as vital to the NHS’s efforts to tackle Covid-19 were badly built, unsuitable for use in hospitals and potentially dangerous for patients, it has emerged.

All of the devices in a consignment of 250 ventilators that arrived from China on 4 April posed such serious problems that they could not be used and were ditched.

Doctors in NHS hospitals in the West Midlands, among which the ventilators were shared, were so concerned that they wrote to Matt Hancock, the health secretary, warning that they could kill patients.

“We believe that if used, significant patient harm, including death, is likely,” they wrote in a letter, which was obtained by NBC News. “We look forward to the withdrawal and replacement of these ventilators with devices better able to provide intensive care ventilation for our patients.”

The medics warned the Department of Health and Social Care that the oxygen supply in the devices was “variable and unreliable”, their build quality was “basic”, the oxygen connection base was marked as “non-EU” and their fabric case made them hard to clean.

The machines were Shangrila 510 ventilators made by Beijing Aeonmed, a major manufacturer of ventilators in China. They were designed for use in ambulances not hospitals, the doctors said.

The day they arrived, Michael Gove, the Cabinet Office minister who is helping to co-ordinate the government’s response to the pandemic, thanked China for sending them.

“We’ve been buying invasive ventilators from partners abroad, including Germany and Switzerland, and today 300 new ventilators arrived from China. I’d like to thank the Chinese government,” he said at the government’s daily news conference, in comments that were widely reported.

However, hospitals that then received the devices could not get them to work, despite technical staff spending several days trying to do so. A senior official at one of the hospitals involved said: “All of the ventilators failed. Nothing worked. They didn’t have proper oxygen centres and the tubing didn’t fit. We were irate. All the hospitals tried to get them to work but we couldn’t.

“At the time we were really worried, because we feared that hospitals were going to be overwhelmed with patients with Covid-19 needing to be ventilated. Happily, as it turned out we didn’t get quite as many as originally expected so we didn’t need the Chinese ventilators after all, which is just as well.”

The ventilators were part of a government drive to increase the NHS’s supply of ventilators from the 8,000 it had before the virus struck, to 30,000, so that anyone needing one during the expected peak of the pandemic could have one while in intensive care. However, that target has since been reduced as hospitals have been able to manage the number of people with Covid-19 needing their care.

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A well-placed NHS source said the incident highlighted problems that had occurred with a range of medical supplies and equipment ordered from China during the coronavirus pandemic.

“Some other stuff ordered from China recently, especially personal protective equipment, has also turned out to be either of a lesser quality than what we need or to be the wrong thing altogether, like T-shirts instead of long-sleeved surgical gowns,” they said.

“You have to be careful who you procure stuff from, because the supply and then what ultimately arrives can be very variable. But, then again, we didn’t have enough ventilators to start with because the government was unprepared for coronavirus, so we had to ask China to help.”

NBC News reported that it approached the international sales manager for Beijing Aeonmed, who said: “I don’t know,” when asked whether the company was aware of the concerns about its product, before the call ended.

A government spokesperson said: “The Shangrila 510 ventilator model is not being used in hospitals and no patients are at risk. Ventilators need to pass robust regulatory tests to ensure they are up to standard before they’re delivered to NHS hospitals.

“Our absolute priority in this global pandemic is saving lives and we are increasing our provision of ventilators to ensure the NHS continues to have the resources it needs, through procuring more ventilators from overseas, including over 4,000 from China, scaling up the production of existing or modified designs and working to design and manufacture new devices. We currently have around 10,900 mechanical ventilators available to NHS patients across the UK, as well as 4,300 non-invasive ventilators.”

• This article was amended on 1 May 2020 to include a comment from a government spokesperson.