At least 235 people have been killed after suspected militants set off a suicide bomb and opened fire at a mosque in Egypt's  restive northern Sinai province. 

The attack on Friday targeted supporters of the security forces attending prayers there, two eyewitnesses and a security source said.

Four off-road vehicles arrived at Al Rawdah mosque in Bir al-Abed, near Arish city, during the sermon section of prayers. Survivors told local media that those who were not killed in the blast and tried to run away were gunned down. 

Unverified pictures on social media showed dozens of bodies, clothes soaked with blood, laid out on the mosque's floor.  Others showed ambulances lining up at the mosque's entrance to take the wounded to nearby hospitals. 

Death tolls from the attack vary. A health ministry spokesperson initially said that 235 people were killed, adding it is feared the casualty count will rise. State media reported that 125 people had been injured. 

While no claim of responsibility has yet been made, Egypt has been fighting a vicious Isis-affiliated insurgency in the Sinai since 2014. Extremism there has flourished in the chaos that has engulfed the country since the 2011 revolution.

Friday's attack comes after a spate of recent bombings targeting the police and army in Sinai and is the deadliest to hit civilians in the area in the last three years. 

While most militant attacks target the security forces, civilians are often caught up in the violence.  Militant attacks outside the peninsula in the rest of Egypt have targeted the country's Christian minority. 

President Abdel Fattah al Sisi has convened an emergency security cabinet meeting in Cairo.