Sharara's production had recovered to 213,000 barrels per day (bpd) by Sunday, when the latest stoppage began. The new blockade led the National Oil Corporation (NOC) to declare force majeure on loadings of Sharara crude from the Zawiya export terminal, the oil source said.
Libya's national production has more than doubled since last year after a blockade at major eastern oil ports ended, but the oil sector continues to suffer from frequent disruptions due to armed conflict, political rivalries and local protests.
Groups with financial or political grievances have often closed oil facilities to make demands for salary payments or funds for local development.
In March the pipeline leading from Sharara was blocked for a week, triggering force majeure on shipments.
The NOC was hoping to boost output from Sharara to 270,000 bpd later this month. The field is operated by the NOC in partnership with Repsol, Total, OMV and Statoil.
Before the new shutdown at Sharara, the NOC said national production stood at 703,000 bpd.
It was aiming to raise output to 1.1 million bpd by August, but acknowledged that such targets depend on the corporation receiving money for its operating budget and oil facilities staying open.
"NOC faces huge challenges including the regularity of NOC's obtaining of employees' salaries in full and in a timely manner, the budgets related to maintenance operations, the blockades, and military actions which hinder production," NOC said in a statement last week.
It also cited "some parties' offering money to some militias, which encourages others to follow blockade tactics to blackmail the state".
A Libyan shipping source said no oil tankers were currently at Zawiya nor were any expected to arrive in the near future.
A preliminary loading schedule for Sharara crude in May seen by Reuters showed eight tankers were expected to load around 600,000 barrels each throughout the month.
In addition to providing an export stream, the oil field feeds the 120,000 bpd Zawiya oil refinery, Libya's largest operating plant.
During a two-year shutdown of the field which ended in late 2016, the refinery ran on reduced rates as it had to rely on NOC shipping crude to the site by sea from other oil terminals.