"There is anger among people against Congress, and if we cannot convert it into votes it will be difficult to take forward the party. This is an opportunity. There is public anger against Siddaramaiah government. There is no better opportunity to convert this anger into votes," Mr Shah said.
Addressing those in charge of BJP's "Shakti Kendra" in Udupi, he said BJP had been winning polls in several states and increasing its tally and "it is Karnataka's turn now."
"Karnataka BJP workers have to make sure that this victory march of Narendra Modi enters southern India through the state," said Mr Shah, who has been on a tour of Dakshina Kannada and Uttara Kannada districts since Monday.
"I have seen and fought all these elections closely," he said.
"BJP has not just won elections. Winning just elections is easy as there will be a wave or some one's fault or anti-incumbency, but BJP along with winning elections has also worked for strengthening the party from deep bottom," he said.
Mr Shah recalled the contribution of party workers with whose efforts BJP had earlier formed the government in the state in 2008 and said after the exit of the BJP government, "there was this corrupt government by the Congress."
He said BJP had not taken short cuts like Congress to win elections and lakhs and lakhs of party workers had put in hard work from the booth level.
Stressing the need for strengthening the party at the booth level, Mr Shah said if this didn't happen, "government can just come and go, but can't continue like in Gujarat and Madhya Pradesh."
He also asked BJP workers not to take party work lightly, and said response from people for the BJP is good.
But he had no hesitation in saying that reports that he has got about ground level work by workers was disappointing, Mr Shah said.
The BJP leader pointed out that the party's success in Manipur and Uttar Pradesh was because of booth level strengthening of the party.
Asking the party workers to strengthen the organisation at the booth level, he said he would come for review at the district level next.
Shah cut short his visit and skipped engagements at Kumta and Gokarna in Uttara Kannada district and left for Delhi due to fever.
"Shah is suffering from high fever and had to go back from Honnavara following doctor's advice," BJP MP Shobha Karandlaje told a large gathering of party workers at Kumta.
Mr Shah was on a three-day visit to the communally sensitive districts of Dakshina Kannada and Uttara Kannada, where the BJP is on a strong wicket and is trying to widen the base further.
Earlier in the day, Mr Shah visited the famous 800-year-old Krishna Mutt at Udupi.
Last night, the BJP president also held talks with senior pontiff of Udupi Pejawar Mutt Sri Visweshatheertha Swamiji.
At Honnavara in Uttara Kannada, Mr Shah visited the family of BJP worker Paresh Mesta, who was found dead under mysterious circumstances in a lake in the district after he went missing, triggering violence.