China has sold nearly four billion masks to foreign countries since March, officials said, as they tried to stem widespread fears over the quality of medical exports.

Despite Chinese cases dwindling, Beijing has encouraged factories to increase production of medical supplies as the pandemic kills over 60,000 globally and parts of the world face a protective equipment shortage.

China has exported 3.86 billion masks, 37.5 million pieces of protective clothing, 16,000 ventilators and 2.84 million Covid-19 testing kits since 1 March, customs official Jin Hai said, with orders to more than 50 countries.

She added the country's medical supply exports were valued at 10.2 billion yuan (€1.4 billion).

However numerous nations - including the Netherlands, the Philippines, Croatia, Turkey and Spain - have complained about substandard or faulty medical products shipped from China.

Last week, the Dutch government recalled 600,000 masks out of a Chinese shipment of 1.3 million that did not meet quality standards.

China said the manufacturer "stated clearly that (the masks) are non-surgical."

Spain also rejected thousands of rapid test kits sent by an unauthorised Chinese company after it found that they were unreliable last week.

Chinese officials hit back at media reports over defective medical supplies, saying that they "did not reflect the full facts".

"In reality there are various factors, such as China having different standards and different usage habits to other countries. Even improper use can lead to doubts over quality," said Jiang Fan, an official with the Ministry of Commerce.

The comments echoed remarks from Foreign Ministry spokeswoman Hua Chunying, who over the past week has repeatedly urged Western media not to "politicise" or "hype up" the issue.

Earlier this week, Beijing tightened regulations for exported coronavirus medical equipment, requiring products to fulfil both domestic licensing standards and that of their destination countries.

China has also increased its production capacity of Covid-19 testing kits to over 4 million a day, said Zhang Qi, an official with the National Medical Products Administration.

China has reported 30 new Covid-19 cases yesterday - up from 19 cases reported the previous day.

The National Health Commission said that 25 of the latest cases involved people who had entered mainland China from abroad compared with 18 such cases a day earlier.

China has become concerned about recent increase in imported cases of Covid-19

Five new locally transmitted infections were also reported, all in the southern coastal province of Guangdong.

Mainland China has now reported a total of 81,669 cases, while the death toll has risen by three to 3,329.

Though daily infections have fallen dramatically from the height of the epidemic in February, when hundreds of new cases were reported daily, Beijing remains unable to completely halt new infections despite imposing some of the most drastic measures to curb the spread of the virus.

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The so-called imported cases and asymptomatic patients i.e. those who have the virus and can give it to others but show no symptoms, have become among China's chief concerns in recent weeks.

The country has closed off its borders to almost all foreigners as the virus spread globally.

However, most of the imported cases involve Chinese nationals returning from overseas.

The central government also has pushed local authorities to identify and isolate the asymptomatic patients.

The health commission said 47 new asymptomatic cases were reported in the mainland on Saturday, compared with 64 a day earlier.