Vice President Mike Pence called Tuesday for construction companies to donate protective masks to hospitals, in a stark sign of dwindling supplies in the U.S. healthcare system.

“We would urge construction companies to donate their inventory of N95 masks to your local hospital and forgo additional orders of those industrial masks,” Pence said at a White House briefing. “Those industrial masks that they use on construction sites are perfectly acceptable for healthcare workers to be protected from a respiratory disease.”

Some hospitals and former health officials have reported low supplies. “Doctors in Denver where the virus hasn’t been yet say they are almost out of masks,” Andy Slavitt, the former head of Medicare and Medicaid during the Obama administration, tweeted Monday.

“Current mask producers could make more, and there are some dormant factories,” Slavitt said. “The government must tell them now that they will pay for them.”

Former FDA chief Robert Califf called for a World War II-style mobilization to produce more protective gear. “We have a current shortage and a looming crisis,” he tweeted. “Why not set up manufacturing sites like munitions and clothes in WW2 and pay people otherwise sidelined to mass produce?”

On Monday, Peter Navarro, a trade advisor to the White House, said mask manufacturer Honeywell had offered to produce more masks at a facility in Smithfield, R.I. “with a little help from the government.” Honeywell said it could begin that production “within 30 days,” Navarro told CNBC.

Eric Krantz, a spokesman for Honeywell of Charlotte, N.C., said the company should finalize that contract with the government soon. He declined to quantify how many extra N95 masks Honeywell could produce, saying the company doesn’t disclose production details “for competitive reasons.”

Jennifer Ehrlich, a spokeswoman for Minnesota-based 3M, said the company has increased production of N95 masks at its factories in the U.S., China, Europe and Latin America.

She declined to quantify the increase, or to provide details on the resources 3M is dedicating to the effort. “Manufacturing capacities of specific plants and products, as well as specific sales volume and customer information, are 3M confidential information that we do not publicly disclose," Ehrlich said.

3M is dedicating more of its output to healthcare workers than to industrial customers, she added.

Erica Lewis, a spokeswoman for Cardinal Health, an Ohio-based distributor of healthcare supplies, said the company’s masks, gloves and face shields “are on allocation, which means that we will supply volume based on recent historic customer needs.”

“Our mitigation efforts include building contingency plans with our existing suppliers, aggressively exploring new sourcing partners, and assessing capabilities and capacity within our manufacturing network to increase production,” Lewis said by email.

A reliance on Chinese factories has exacerbated the supply problems. China’s widespread shutdown of factories as the country battled its own coronavirus outbreak has stopped some protective gear from reaching the U.S. market.

Medline Industries, a healthcare distributor based in Northfield, Ill., said factories it relies on in China’s Hubei Province, where the outbreak began, are now re-opening.

“After almost two months of a manufacturing hiatus, China re-opened manufacturing operations in the Hubei Province on March 10 as hoped," Medline spokesman William Berger said by email. “However, the production ramp-up at these factories is expected to be slow. The result is a reduction in capacity and delayed shipments from factories.”

“We have put in place inventory management programs and allocations to protect as much inventory as possible for our customers. In addition, we are actively working on options to increase production in other areas of our global supply chain, while diligently monitoring the situation in Southeast Asia,” Berger said.