The Kenya Wildlife Service (KWS) says it has contained a huge fire which started on Saturday afternoon at Tsavo National Park.
The KWS blamed arsonists and police say they are pursuing suspects.
Hundreds of local volunteers and the military took part in putting out the fire.
Tsavo, in south-eastern Kenya, is the country's biggest national park and home to hundreds of animals such as lions, elephants and buffaloes.
It is visited by thousands of local and international tourists each year.
The fire came at a time when the Kenyan government is pushing for a revival of the crucial tourism industry which has lost $1bn (£770m) in revenue due to Covid-19.
KWS described the fire as "horrendous" and thanked the hundreds of volunteers trying to put out the fire.
"Your efforts and sacrifices are appreciated beyond words," the service said on Twitter.
The military used helicopters to pour water on the fire.
In July, several fires ravaged the Tsavo area.
"The combination of long rains earlier in the year, which saw grasses grow tall, strong winds and inaccessible areas have made this a high fire risk period in Tsavo," a conservation group called the Sheldrick Wildlife Trust explained in July.
The trust tweeted a video of their efforts to put out those July fires:
It's out. A sweeping bush fire in Tsavo West National Park, Kenya finally extinguished after 3 days thanks to a mammoth effort by KWS, community and conservation groups. Read more: https://t.co/ID1nGnxFg7 pic.twitter.com/lS5sB2p1TI— Sheldrick Wildlife (@SheldrickTrust) July 27, 2020