"Evacuation teams are working tirelessly to rescue the injured," said Ugandan police spokeswoman Emilian Kayima, adding that all three drivers had died.
Emilian Kayima says in a statement that 14 people were injured.
"The death toll is now at 48 including 16 children," Red Cross spokeswoman Irene Nakasiita told AFP.
The accident occurred in Kiryandongo, about 220 kilometers (140 miles) north of the capital Kampala.
Kiryandongo accident involving Gaga coach and a heavy duty fuso lorry last night claimed over 40 lives.#Tweddeko Speed kills @VivoEnergyUg @ntvuganda @UNRSC @KampalaTraffic @robert_kwesiga @inakasiita1 pic.twitter.com/sBjQiNtmbZ— Uganda Red Cross Soc (@UgandaRedCross) 26 мая 2018 г.
According to police, the tractor was driving without lights, which may have been the cause of the accident.
Uganda is among the countries that have the worst traffic safety, due to poor conditions of roads and vehicles, as well as hazardous driving.
The police statement says "many road accidents are a result of avoidable human undertakings."