The city has seen more than 100 new cases in the fresh outbreak, the World Health Organization (WHO) says.
For more than seven weeks Beijing had only registered cases from people travelling in from abroad.
New clusters of coronavirus are "always a concern", said Mike Ryan, the WHO's emergencies programme head.
"But what we do like to see is an immediate response to that and comprehensive set of measures," he added.
What do we know about the new cases?
The fresh outbreak has been linked to city's largest wholesale market, Xinfadi.
Local media reports say the virus was discovered on chopping boards used for imported salmon at the market, prompting major supermarkets in Beijing to pull the fish from their shelves.
The general manager of the market has been dismissed, along with other local officials.
In his comments though, the WHO's Mike Ryan was cautious about the cause of the outbreak, saying the suggestion it was carried on salmon or its packaging was only a "hypothesis".