Peru has sworn in new President Pedro Castillo, a leftist former teachers' union leader who already faces mounting challenges to build his government, tackle the coronavirus crisis and unite a deeply polarised country.

Castillo was sworn in at midday local time (1700 GMT) on Wednesday in the capital, Lima, after weeks of uncertainty following a hard-fought June presidential runoff that saw him edge right-wing rival Keiko Fujimori by about 44,000 votes.

Three days of ceremonies are planned, starting with Wednesday's inauguration on Peru's independence day that will be attended by Spanish King Felipe VI, six Latin American leaders, former Bolivian President Evo Morales, and the United States education secretary, among others.

A military parade is planned for Lima on Friday.

Castillo, a 51-year-old former rural schoolteacher, becomes Peru's first president in decades with no ties to the country's political or economic elite and he has promised, among other things, to ensure there are "no more poor people in a rich country".

(With input from agencies)