A man was stabbed and seriously injured in Jaffa, near Tel Aviv, on Wednesday afternoon, police and medics said.
The circumstances of the assault and the identity of the victim were not immediately clear.
Police said the perpetrator was a Palestinian who entered Israel illegally and was arrested. Police said the motive was apparently a terrorist attack and identified the victim as a resident of Jaffa.
However, Magen David Adom rescue services identified the victim as a 49-year-old East Jerusalem resident.
MDA said he was taken to Wolfson Medical Center in Tel Aviv in serious condition with stab wounds.
Police photos appeared to indicate the man was stabbed with a screwdriver while fishing.
Police said they were searching the area for other suspects.
The attack comes with forces on high alert on the eve of Yom Kippur, the Jewish Day of Atonement and the holiest day in the Jewish calendar.
There have been a spate of stabbing attacks in recent days, apparently in solidarity with six Palestinian security prisoners who escaped from Gilboa prison last week. Two of the six are still at large.
In Jerusalem, some 2,000 police were deployed, with roadblocks and checkpoints set up around the old city, as thousands of worshipers were expected at the Western Wall. Police were also monitoring places of worship across the country.