Egyptian police have stormed the press syndicate in Cairo and arrested two journalists critical of the government, a syndicate official and reporters said in what the union called an unprecedented crackdown.

The interior ministry denied officers stormed the press labour union building, a traditional spot in downtown Cairo to stage protests, but confirmed some of its members had arrested the journalists inside the syndicate on Sunday.

Security forces have sought to quell dissent since thousands took to the streets on April 15 to protest against President Abdel Fattah el-Sisi's government.

On Sunday, journalists held a sit-in inside the union when officers arrested two of them. Both of the detained work for the opposition website Bawabet Yanayer, and one is its editor, syndicate officials said.

"The incident is true, and at the very least the interior minister has to be fired and there needs to be an apology," Khalid al-Balshy, a syndicate board member, told the Reuters news agency.

Mahmoud Kamel, another member of the syndicate board, said more than 40 policemen stormed the building but the interior ministry said its force consisted of just eight officers.

"The ministry affirms that it did not raid the syndicate or use any kind of force in arresting the two journalists, who handed themselves in as soon as they were told there was an arrest warrant," the interior ministry said in a statement.

A security guard was wounded in the eye when police raided the union, Kamel said.

"There was an arrest warrant for the two journalists issued a week ago but the syndicate was negotiating with the interior ministry over the matter," he said.

Under the law only a prosecutor is allowed to search the union in the presence of its chairman or deputy, he added.

"This is unprecedented. No president or prime minister or interior minister has ever dared to do something like this," Kamel said.

Call for strike

The syndicate council called for an indefinite strike among Egyptian journalists until the interior minister resigned and urged newspapers to black out their front pages.

Dozens of journalists later held a new sit-in at the syndicate to protest against the arrest, a reporter said.

An Egyptian court on Saturday imposed a media gag order on the case of protesters arrested during demonstrations against a demarcation deal that handed over two Red Sea islands to Saudi Arabia.

Scores of people have been arrested in Cairo and other places over the past two weeks during protests, as well as from their homes and in cafes.

Sisi has faced criticism over the demarcation deal and a faltering economy but there are no signs that his rule is under threat.

The Committee to Protect Journalists says Egypt is second only to China as the world's worst jailer of journalists, holding at least 23 journalists in jail.