"Our hearts go out to all those in Australia affected by these devastating fires. I have been in touch with [Australian Prime Minister] Scott Morrison to offer any assistance we can provide. We stand with you at this very difficult time," Johnson wrote on Twitter.
On Monday, Morrison pledged to allocate 2 billion Australian dollars ($1.4 billion) to help his country through the newly-established National Bushfire Recovery Agency.
The Australian prime minister specified that this new commitment would come in addition to the government's emergency and disaster payments and support for volunteer firefighters.
On Monday, media reported that the bushfires in Australia, which have claimed at least 25 lives and have destroyed over 1,000 houses, are expected to burn for months to come.