The Sh1.2 billion Sigiri Bridge, under construction in Budalang'i constituency, Busia County, collapsed in unclear circumstances.
Some 27 workers were injured when the bridge came down tumbling in the morning incident. Twenty-five were treated at Port Victoria Hospital and discharged while two, who suffered serious injuries, were admitted in Nangina Mission Hospital.
County Police Co-ordinator Elisha Odhiambo warned members of the public against approaching the collapsed bridge, which was due for completion next month.
The incident comes 11 days after President Uhuru Kenyatta and his deputy William Ruto inspected the bridge being built by China Overseas Engineering Co.
The Government said it had dispatched a team of top engineers to investigate the cause of the collapse.
Infrastructure Principal Secretary John Mosonik said Kenya Rural Roads Authority was also planning a "detailed geo-technical and structural investigation to establish the cause of the (structural) failure".
He said construction activities on the site had been suspended until an integrity report was ready.
"The ministry has also contacted the investigative arm of Government to look into the matter to rule out any possible foul play," Mr Mosonik added.
The collapse affected the middle span of the bridge, which was 50m long. The others were 25m apiece.
The Opposition National Super Alliance (NASA) alleged the collapse was evidence that Jubilee government projects were meant for enriching individuals.
"The embarrassing collapse exposes the fact that the Sh1.2 billion was for siphoning off public funds rather than putting up a quality bridge," said NASA National Campaign Committee member Kibisu Kabatesi in a statement.
Mr Kabatesi challenged Jubilee to tell Kenyans why quality and safety were not guaranteed. And during a tour of Busia on Sunday, NASA presidential flag bearer Raila Odinga had accused Uhuru of taking credit for a project that was his (Raila's) brainchild.
The bridge connects Bunyala South and Bunyala North wards. Uhuru ordered construction in 2014, after nine people died while crossing River Nzoia.