China’s foreign ministry is disputing Prime Minister Justin Trudeau’s contention that restrictions on how much time a cargo jet can spend on the ground in Shanghai played a part in why two aircraft returned to Canada without medical supplies.

Mr. Trudeau, asked to explain why two planes chartered by Canadian governments to procure medical gear from China instead came home empty, on Tuesday first cited limits on the amount of time a plane can spend on the ground .

“There are severe restrictions on the ground in China in terms of how long a plane can actually stay in their airports before having to leave – whether it’s full or not,” Mr. Trudeau said Tuesday.

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It was not the only explanation he gave. Mr. Trudeau also noted that “supply lines and shipments to the airport are difficult and interrupted by checkpoints and quarantine measures.”

In Beijing, however, a spokesman for China’s Ministry of Foreign Affairs on Wednesday denied there are limits on ground time for cargo jets in Shanghai. He was responding to a question about Mr. Trudeau’s comments on Tuesday.

“As to the incident involving two Canadian flights returning empty, we have checked with the competent department and found relevant reports to be inaccurate,” Geng Shuang, a spokesman for the foreign ministry, told a press briefing.

“Relevant airports and civil aviation authorities place no limit on the ground time of chartered cargo planes.”

One of the two planes was chartered by the Canadian government while another plane, according to Mr. Trudeau, had been hired by a province which he declined to identify.

Mr. Trudeau was not the only Canadian official Tuesday who offered explanations for the shipping snafu.

The same day, Cecely Roy, press secretary to federal Public Services and Procurement Minister Anita Anand, provided additional information on what happened, saying traffic flows prevented the federal aircraft from picking up its load before it was obliged to leave.

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“This occurred due to on-the-ground congestion caused by a significant surge in cargo flights out of terminals at the Shanghai Airport. As a result, the intended cargo was unable to get to the plane before its required takeoff time.”

The Canadian government on Wednesday declined to respond directly to the Chinese government’s denial about ground limits on cargo jets.

“Canadian officials are working closely with Chinese authorities as part of our efforts to ensure that Canada has the medical supplies that we need in the fight against COVID-19. We appreciate their collaboration as we navigate the complexity of logistics on the ground with high global demand,” Ms. Roy said.

On Wednesday, China’s Mr. Geng also noted that China and Canada have been offering each other support and assistance to fight COVID-19

“Recently, the Canadian side has purchased medical supplies through various channels in China and sent charter flights to Shanghai to bring them home. China has been assisting and facilitating the Canadian side in its purchase, customs clearance and charter flight permits. The Canadian side has also expressed thanks for this on various occasions.”

Many U.S. states – where COVID-19 has hit hard – are competing with other countries to buy medical gear, from face masks to medical gowns to gloves and thermometers, and they have turned to aircraft rather than ships to speed delivery from China. A report by Shanghai Daily’s Shine publication on April 15 said more than 200 cargo flights from around the world landed and took off from the city’s Pudong Airport in recent weeks, loading up 10,000 tonnes of medical gear.

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Ms. Anand’s office on Tuesday also said Canadian officials are taking steps to ensure planes do not return empty and noted that four other flights arrived on the weekend from China with medical supplies such as N95 respirator masks, protective coveralls and chemical compounds needed for testing.