The U.S. expressed "grave concern" Monday over the situation in Hong Kong after police opened fire on protesters, critically injuring one.

"The United States is watching the situation in Hong Kong with grave concern. ‎We condemn violence on all sides...and call for all parties — police and protestors — to exercise restraint," said State Department spokeswoman Morgan Ortagus in a statement.

One of the protestors was shot in the abdomen in the Sai Wan Ho area of the once vibrant business city. He is reportedly in critical condition.

Hong Kong , an semi-autonomous region under China since July 1997, has been witnessing protests since early June against the Carrie Lam administration’s move to legalize extradition to mainland China.

The bill to amend the extradition law was finally withdrawn on Sept. 4, but people are still upset and want Lam to meet other demands.

"The United States urges the Hong Kong government to build on its dialogue with the Hong Kong public and begin efforts to address the underlying concerns driving the protests," said Ortagus. "We also urge the protestors to respond to efforts at dialogue."

Monday's incident follows a student's death last Friday after he fell in a car park during a police dispersal operation in the Tseung Kwan O area, where security forces had fired tear gas.

Protests have left the city reeling for months, with international financial observers downgrading their economic forecasts for the business hub.‎