His office said it was a "precautionary step", not an emergency admission.
"On the advice of his doctor, the Prime Minister has tonight been admitted to hospital for tests," Downing Street said on Sunday.
"This is a precautionary step, as the Prime Minister continues to have persistent symptoms of coronavirus 10 days after testing positive for the virus."
On March 27, Johnson became the first leader of a major power to announce that he had tested positive. He went into isolation at a flat in Downing Street and said on Friday that he was staying there as he still had a high temperature.
Johnson has continued to chair daily meetings on the UK's response to the outbreak, and has released several video messages during his 10 days in isolation.
In a message on Friday, he said he was feeling better but still had a fever.
Johnson remains in charge of the government, Downing Street said.
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