China has sold nearly four billion masks to foreign countries since March to curb Coronavirus spread, officials said Sunday.

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 March 1, customs official Jin Hai said, with orders to more than 50 countries.

She added that the country’s medical supply exports were valued at 10.2 billion yuan ($1.4 billion).

However, many of the importing countries 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 on Sunday 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.

Earlier this week, Beijing tightened regulations for exported coronavirus medical equipment, requiring products to fulfill both domestic licensing standards and those 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.