The Tories know they will need to win these seats to secure a majority in the House of Commons as the fate of Brexit is on the line.
Sunderland - a traditional Labour stronghold that hasn't elected a Tory MP since 1959 - was Mr Johnson's first stop. He told voters there on Monday that the Labour Party has let them down.
The Prime Minister also criticised the Parliament calling it "broken".
"This is a broken Parliament that will not allow the people of this country to have their voices heard", Johnson said in his speech in Sunderland. "It will not allow the people of this country to express their will. They expressed it three years ago".
Sunderland was also the first area in the 2016 referendum to vote in favour of UK leaving the EU - 61,3% voted to Leave there.
Dr James Downes, a professor in comparative politics at the Chinese University of Hong Kong, says it's the Conservative Party strategy "to eat into the core voter base of the centre-left UK Labour Party".
"Traditionally in British politics, the working classes voted for Labour, while the middle and higher upper classes voted for the Conservative Party. Fast forward fifty-two years and this is no longer the case", the expert explained.
Dr Downes also noted that in recent years Labour had been threatened in its traditional northern heartlands not just by the Tories, but also by the now "obsolete" UKIP Party and the Brexit Party.
"Recent findings have demonstrated how the Conservative support amongst the working classes is now 10% more than the Labour Party is. This finding (if it holds up in a few days when British voters go to the polls) is staggering and demonstrates just how far Labour has fallen in representing their working-class voter base. The party faces a major dilemma regarding their future strategy and way forward", the professor said.
The other issue that's causing the opposition to lose its votes is Brexit. And Dr Downes has blamed Labour leader Jeremy Corbyn's unclear stance on UK's departure from the EU as the reason for this.
"This has arguably hurt the Labour Parliamentary Party and angered its core working class-based voters", he said.
According to the latest YouGov poll (5-6 December), Conservatives currently have a substantial lead over Labour. Johnson's party is at around 43% in poll ratings, and while Labour has been rising in the polls, it is still at only about 33%.
Latest Westminster voting intention (5-6 Dec)
— YouGov (@YouGov) December 8, 2019
Con - 43%
Lab - 33%
Lib Dem - 13%
Brexit Party - 3%
Green - 3%
Other - 5%https://t.co/tnX5u6TSfU pic.twitter.com/eegBRQLuox
Dr Downes pointed out that the electoral decline of the social democratic parties is a trend that can be seen across Western Europe and is not just confined to British politics.
These parties are now losing support to both radical right and left-wing parties alike. "Two key events in the form of the 2008-2013 economic crisis and the ongoing migration crisis have further precipitated the electoral slide of social democratic parties across Europe", the professor stated.
He also predicted that this volatility is likely to continue in the coming years for the social democratic parties.
"If the UK Labour Party do lose the General Election this week resoundingly to the Conservatives, the very survival for the future of the Labour Party is in doubt", Dr Downes concluded.
British parties are in the final days of their election campaign ahead of the December 12 snap general election that was initiated by Johnson and his Conservative party after struggling to get support for his Brexit deal in Parliament.
Polling stations across the UK will open on Thursday at 9 am and close at 10 pm local time. The vote counting will begin straight away and the results are expected to be announced in the early hours of Friday morning.
