A fire damaged stalls at Uhuru market along Jogoo Road in Nairobi from about 6 pm on Monday.
Trader Weston Gisamu said it started in a stall.
“The fire brigade are here … we hope it will be contained before it is too late,” he said on phone.
The cause was not established immediately.
Traders lost their property in a similar incident at the market in 2011.
In June, 16 people died while more than 50 were injured in a fire at Nairobi’s Gikomba market.