The well-supplied gasoline market also looked to shutdowns and increased summer demand to help boost prices.

Wholesale gas oil, or diesel, were 3,700 to 3,850 yuan ($447- $465) per tonne on the east coast consuming centres, up almost nine percent from earlier in the month, tracking the increase in retail rates imposed by Beijing effective from mid-May.

"Prices could head even higher if Beijing allows them to, because supplies will be tightened further with refinery shutdowns," said a marketing official with Sinopec Corp (0386.HK: Quote, Profile, Research) (SNP.N: Quote, Profile, Research) , Asia's top refiner.

Sinopec will be shutting down crude distillators and secondary units at four main coastal plants in June at Zhenhai (1128.HK: Quote, Profile, Research) , Jinling, Gaoqaio and Guangzhou (please read table of Asia Refinery Maintenance [ID:nSP233314]).

Second-largest refiner, PetroChina (0857.HK: Quote, Profile, Research) (PTR.N: Quote, Profile, Research) , also planned to repair a crude unit late in June at northeast China's Jinzhou plant (for story, click on [nPEK10663])

The turnarounds, mostly planned, came at a time of worsening electricity shortage as summer air-conditioning stretched the national power grid and spurred the use of single diesel-fired generators.

Officials largely shrugged off the impact of the annual fishing ban on the domestic market. The ban affecting the coastlines off Zhejiang and Fujian provinces, which will start on June 16, has been extended to three months from last year's two months.

A total of 120,000 vessels will be kept in port by that move, together with another ban from June 1 to August 1 on the southern coast off Guangdong and Guangxi provinces as well as Hong Kong.

These boats, the main conduits of smuggled diesel from abroad, also get their supplies from small local Chinese refineries, which are normally cheaper than those sold by state refiners.

To boost thin domestic inventories, China has imported 90,000 tonnes of gas oil in June, keeping up their recent purchases, which have turned China into a net importer from exporter.

Official customs data showed China's imports rallied 80 percent to around 580,000 tonnes in the first four months from year-earlier levels.

GASOLINE FLAT, FUEL OIL TANKS FULL

Gasoline prices held mostly flat from about three weeks ago with benchmark 90-octane quoted at 3,950-4,050 a tonne.

Distributors hoped that next month's refinery shutdowns and steady export volumes could keep recent ample supplies in check and bolster prices further at a time of increased seasonal demand.

"We are already seeing more gasoline sales as cars turn on aircons," said the Sinopec marketing official.

China's gasoline exports (CN/OIL4: Quote, Profile, Research) had fallen sharply to fuel a domestic car boom. However, it was forecast to keep June overseas sales steady from May at about half a million tonnes.

China's domestic fuel oil prices were under heavy pressure from bumper purchases in the first months of the year (CN/OIL8: Quote, Profile, Research) , forcing importers to slash May purchases into the leading Huangpu terminal by around 30 percent versus April.

Cracked 180-centistoke material was pegged at 2,020 yuan per tonne, slipping from 2,090 yuan levels earlier in the week.

Imports by Asia's largest fuel oil buyer jumped 64 percent from a year earlier to 10.2 million tonnes in the first four months, partly driven by the country's soaring gas oil market, which sucked in nearly 40 percent of heavy refinery product that can be processed into diesel.