Mr Johnson labelled the reports as “appalling” as he visited Birstall with Conservative candidate Ryan Stephenson on Monday. Mr Stephenson is ahead in the polls as he bids to win a seat held by Labour since 1997.
The PM told reporters on a visit to PPG Architectural Coatings: “I find it utterly sickening and appalling that some people choose to campaign in this way.
“We in the Conservative party, Ryan Stephenson is campaigning on a positive message for change and progress in Batley and Spen, bringing people together."
Newly-elected West Yorkshire mayor Tracy Brabin said she was leafleting with “colleagues, volunteers, campaigners” who “were followed, verbally abused and physically assaulted by a group of young men” in the Whitaker Street area of Batley on Sunday.
Ms Brabin - the seat’s former Labour MP - described people “being egged, pushed and forced to the ground and kicked in the head”.
Earlier, Labour’s candidate and sister of murdered MP Jo Cox, Kim Leadbeater, was seen on video being confronted by a man who challenged her over the situation in Kashmir and her stance on LGBT+ education in schools in light of what he said were concerns from Muslim parents.
Last week it was reported that the Tories are polling at 47 per cent in the seat that has been held by Labour for almost 25 years, but Mr Johnson described the contest as "a tough fight."
He told reporters: "We’re fighting for every vote and as we do everywhere I think we have to recognise that Batley and Spen has been held by Labour for decades and it’s going to be obviously a tough fight, that's clear.
"But I think Ryan has a fantastic positive message for change and it only takes 1,763 voters to go with the Conservatives, go for change, and what I think is positive progress in Batley and Spen."
Labour leader Sir Keir Starmer has also condemned as "disgraceful" the abuse Ms Leadbeater faced while campaigning on Friday.
Ms Leadbeater, was seen to ask the man who confronted her not to shout at her, before turning away and being pursued and heckled by a group. In the video, he raises his voice at Ms Leadbeater, who responds by repeatedly asking why he would shout at her in the street. Ms Leadbeater then leaves and is pursued by a group to a car.
Ms Leadbeater said she is “really disappointed and sad about some of the behaviour that we’ve seen over the last few days” after reports of violence on the campaign trail, but that she will “rise above” the incidents.
She told The Yorkshire Post: “It breaks my heart that our community is under the threat of being divided by people coming here with their own agendas and the verbal abuse that I suffered and the attacks that were perpetrated on activists who have come to this area, doing the right thing, fighting for something they believe in is very upsetting and it worries me the damage that this will do to our community.”
She added: “I really hope that people can be civilised to each other during this last few days of campaigning, I really hope that. That’s certainly how I’ll be approaching the rest of the campaign and it’s about having intelligent conversations with people, it’s about listening to people that’s what this by-election should be about. It’s not about shouting at each other in the streets because what matters is the people of Batley and Spen and that’s absolutely what I’ll be focusing on.”
Her sentiments were echoed by shadow Home Secretary Nick Thomas-Symonds who jointed the Parliamentary candidate in Birstall to knock doors yesterday. “What happened was completely and utterly unacceptable”, he said. “Going out on the doorsteps knocking on doors is a vital part of our democracy and anybody should be able to do that without living in fear.”
With three days left of campaigning, the Labour candidate described herself as “so deeply emotionally invested in this community.” She went on: “That’s why I am just going to rise above the unacceptable behaviour and just try and stay as positive as possible.”
Tensions have been rising in the race - where voters go to the polls on Thursday - which has a total of 16 candidates but is seen as a two-party battle between Labour and the Conservatives.
Former Bradford MP George Galloway is standing for his Workers Party and is seen as a threat to Labour's chances of winning by winning support from sections of the Muslim community.
Stephen Yaxley-Lennon - also known as Tommy Robinson - was reported to be visiting the seat for a rally on Saturday, prompting counter-demonstrations.
But Mr Yaxley-Lennon did not turn up and West Yorkshire Police said that despite around 400 people gathering, demonstrations passed mostly without incident.
A total of three arrests were made - two for public order offences and a man was also arrested for possession of an offensive weapon. Officers also assisted two people who are believed to have suffered medical episodes.
Assistant Chief Constable Scott Bisset, who led the policing operation, said: "Our overall aim was to ensure that the demonstrations remained peaceful and were effectively managed, so that the wider public were able to go about their business unaffected."