A US doctor got a welcome surprise when she was pulled over for speeding by a police officer and instead of a fine, she was given extra face masks.

Cardiologist Sarosh Ashraf Janjua, who is working at a coronavirus quarantine unit in Duluth, Minnesota, took to Facebook to share her story, which she said brought her to tears after being stopped by State Trooper Brian Schwartz for speeding on a highway.

"He went back to his patrol car to look up my licence, and when he returned, quite firmly told me it was very irresponsible of me to be speeding, especially since I would not only take up resources if I got into an accident, but would also not be in a position to help patients," she wrote in a Facebook post.

"As I sputtered to apologise and say thank you, he reached in to hand me what I assumed was my licence back.

"It wasn't until my hand had closed around what he was giving me that its unexpected bulkiness drew my eyes to it.

"Five N95 masks, from the supply the state had given him for his protection."

Cardiologist Sarosh Ashraf Janjua was stopped by a Minnesota State Trooper for speeding on a highway but was given masks instead of a ticket (Facebook)

She was let off with just a warning.

"Thank you to Sarosh for her hard work and dedication," Minnesota State Patrol said on their Facebook page to the thankful cardiologist.

"Troopers are working hard during the pandemic and are thinking about all the first responders who are caring for Minnesotans during this critical time."

As the US face battles on many fronts from the coronavirus pandemic, the dwindling supply of medical supplies in some states worst hit - such as New York - is among the biggest concerns as the death toll rises.

Cardiologist Sarosh Ashraf Janjua took to Facebook to share her story (Facebook)

There have been 3867 deaths in the US from coronavirus, but today top government scientists made a grim estimate that the COVID-19 pandemic could claim the lives of between 100,000 and 240,000 Americans.

The actions of the police officer in Minnesota gave Dr Janjua hope that Americans can work together to beat the pandemic.

"This complete stranger, who owed me nothing and is more on the front lines than I am, shared his precious masks with me, without my even asking," she wrote.

Cardiologist Sarosh Ashraf Janjua was stopped by a Minnesota State Trooper for speeding on a highway but was given masks instead of a ticket (Facebook)