Thousands of members of the Palestinian security forces have begun casting their ballots ahead of the Palestinian election on 25 January.
Security forces are voting early so they can protect polling stations
The security forces are allowed to vote early so they are free for duty when civilians go to the polls on Wednesday.
On Friday, Israel and the Palestinians formally agreed the procedure for voting in occupied East Jerusalem.
Fewer than 6% of East Jerusalem's eligible Palestinian voters will be able to cast their ballots in the city.
The remainder - an estimated 109,000 people - will have to travel to polling stations outside the city boundaries.
Some 60,000 members of the different branches of the Palestinian security forces are eligible to vote from Saturday to Monday.
A steady stream of voters was reported at the 17 polling centres in Gaza and the West Bank on Saturday morning.
Scheduled for 25 January; originally set for July 2005
132 members elected to Palestinian Legislative Council (PLC)
Fatah and Hamas are main contenders
First time Hamas participates in parliamentary poll
Last parliamentary elections held in 1996
"This is a very important day for our people because all the parties are participating," Gaza police officer Hisham Saqala told Reuters.
Army officer Sumaa al-Saudi told AFP news agency: "This is a major political step for the future of our country, a stage in the revolution. This is a step toward reform, a free country and peace."
Dozens of observers from the European Union, human rights groups and political parties are in place to monitor the poll.
The ballots cast over the next three days will be kept locked up and counted at the same time as those cast on Wednesday.
Polls show the militant group Hamas - competing in legislative elections for the first time - close behind President Mahmoud Abbas' ruling Fatah party.
The Israeli government has decided to ban Hamas from campaigning in East Jerusalem and to bar its inclusion on ballot papers distributed there.
Israel has occupied East Jerusalem since 1967. It has annexed the area and sees it as its exclusive domain.
Under international law the area is considered to be occupied territory.
The area is often called Arab East Jerusalem because the majority of its residents are Palestinian, and Palestinians hope to make it their future capital.