Police have detained artist and activist Fahmi Reza for selling #KitaSemuaPenghasut T-shirts featuring a clown-faced Prime Minister Najib Abdul Razak this evening.

Fahmi had earlier promoted his T-shirts at the KL Alternative Bookfest (KLAB) at Publika in Kuala Lumpur.

According to Institut Rakyat executive director Yin Shao Loong three other people were also detained and taken to Sentul district police headquarters under the Sedition Act 1948.

They are event organiser Pang Khee Teik, community activist Lew Pik-Svonn and comic artist Arif Rafhan Othman.

"I am in a police car from Publika to Sentul district police headquarters for questioning for selling #KitaSemuaPenghasut T-shirts during the KLAB 2016.

"Five to six police officers came to my booth just now and confiscated my identity card, two #KitaSemuaPenghasut T-shirts from a bag and a banner featuring a clown face," said Fahmi in a Facebook posting.

"According to the police, I am being investigated under the Sedition Act," he added.

Earlier today, Fahmi handed one such T-shirt to former premier Dr Mahathir Mohamad, who was at the KLAB to officiate a new Dubook Press book titled "Apa Habaq Orang Muda".

He also surprised Mahathir with a colouring book where one of its pages featured the ex-premier holding up his middle finger with the word "Dictator".

Previously, Fahmi was investigated by police for publishing images of a clown-faced Najib which he designed.

He will be charged under Section 233(1) of the Communications and Multimedia Act 1988 for hurting the feelings of other people next week.

However, it is unclear if police intend to press charges in this latest incident.