A Nobel laureate who is in Kerala as a state guest to attend a conference was left stranded for a couple of hours after supporters of Wednesday’s nationwide shutdown stopped his houseboat in the picturesque backwaters of Alappuzha before better sense prevailed.

The boat Michael Levitt had hired was blocked along with several others although the sponsors of the shutdown, called by some central trade unions, had on Tuesday clarified that the state’s tourism sector would not be affected.

Levitt, winner of the 2013 Nobel Prize in chemistry which he shared with two others, described his experience in a message where he said the treatment he received as a state guest was “not good” either for “tourism, the State of Kerala, or the Country of India”.

The Stanford University professor had to wait along with his wife and several other foreign tourists for about two hours before the strike supporters allowed their boat to leave around 12.30pm.

Levitt, who has been to Kerala once earlier, had been invited by the state’s higher education department and Kerala University to attend a conference on the varsity’s campus in Thiruvananthapuram.

In pictures now available on social media, the Nobel laureate can be seen hugging a full-grown fig tree he had planted on his earlier visit in 2010.

On Wednesday, Kerala University professor Achuthsankar S. Nair posted on Facebook a message he received from Levitt after the biophysicist was held up in the backwaters.

Levitt said he had been “warned against protesting to the union people who are illegally enforcing the strike” despite the declaration that “tourism is excepted”.

“Still, this treatment of an official guest of the Kerala State Government is not good for tourism, the State of Kerala, or the Country of India,” he wrote.

Left leaders promised action against those who stopped the boats. State tourism and temple affairs minister Kadakampally Surendran said those responsible would be strictly dealt with.

“We have already initiated action to find out who was behind this even after all trade unions clarified that the tourism sector would not be affected,” Surendran told reporters.

P.P. Chittaranjan, state secretary of the CPM-backed Citu, one of the unions behind the nationwide shutdown, said: “At the moment we don’t know who was behind this. But we will certainly find them.”

Later in the day, police registered a case based on a complaint filed by the owner of one of the houseboats.

The shutdown — called against the Narendra Modi government’s economic policies, changes in labour laws and other steps including the controversial citizenship law, was total in Left-ruled Kerala where all educational institutions, government offices and business establishments remained closed.

But for a few auto-rickshaws at some places, local transport stayed off the roads.

The shutdown in neighbouring Karnataka was partially successful as life was normal in capital Bangalore and most of the southern and coastal districts. But protests were held across the state.

Several IT companies in Bangalore had given employees the option of working from home, fearing disruption in public transport services.