U.K. Prime Minister Boris Johnson was admitted to a hospital for tests Sunday, 10 days after contracting the coronavirus.

A Downing Street spokesperson said it's a "precautionary step" since the prime minister continues to have persistent symptoms of the virus.

"The Prime Minister thanks NHS staff for all of their incredible hard work and urges the public to continue to follow the Government's advice to stay at home, protect the NHS and save lives," the spokesperson said.

Johnson, 55, is the first major governmental leader known to have contracted the disease. He had been self-isolating at in his flat next door to 10 Downing Street and was running a high temperature.

He remains in charge of the government and is in contact with ministerial colleagues and officials.

News of Johnson's hospitalization followed a rare television address to the nation by Queen Elizabeth II, who urged citizens to confront the pandemic with resolve and unity.

"I am speaking to you at what I know is an increasingly challenging time," the queen said in a taped broadcast from Windsor Castle on Palm Sunday.

"A time of disruption in the life of our country: a disruption that has brought grief to some, financial difficulties to many, and enormous changes to the daily lives of us all."

The virus has infected more than 40,000 people in Britain, including the queen's eldest son and heir to the British throne, Prince Charles. He announced two weeks ago that he was suffering with mild symptoms.

Johnson ordered a lockdown of the country on March 20, but initially hesitated to shut down restaurants and bars.

The UK government has been struggling to offer public coronavirus testing. Health Secretary Matt Hancock, who had contracted the virus, vowed that Britain would conduct 100,000 tests a day by the end of April.

According to the government's succession plan, the first secretary of state — 46-year-old Foreign Secretary Dominic Raab — has been designated to take over the duties of prime minister in the event of incapacitation.

On Saturday, Johnson's 32-year-old pregnant fiance, Carrie Symonds, announced on Twitter that she had symptoms of the virus, too. She is expecting the couple's baby in early summer.

Symonds tweet

— CNBC's Marty Steinberg contributed to this report.