At least 20 doctors at a public hospital outside Mexico City have tested positive for the coronavirus, the head of Mexico's social security institute (IMSS) said, in the second major outbreak among health workers in the country.

Coronavirus was first detected at the hospital in Tlanepantla de Baz, in Mexico State just outside the capital, on March 10, IMSS Director Zoe Robledo said at the president's regular news conference.

He said the transmission did not originate inside the facility, and that it had been tracked to three separate cases — one patient and two doctors who did not have contact with each other.